Tracks the camera forward and backward. You can also Alt + right-click (or Alt + left and middle mouse buttons). Use Ctrl + Alt + left mouse button to drag a marquee around the area you want to dolly in on.
To open the Dolly Tool options
Scales the speed of the camera movement. The slider range is 0.01 to 10. The default value is 1.
If on, drag in the camera’s view to move the camera toward or away from its center of interest. If off, drag in the camera’s view to move both the camera and its center of interest along the camera’s sight line. Local is on by default.
If Center of Interest is on, middle-drag in the camera’s view to move the camera’s center of interest toward or away from the camera. If off, drag in the camera’s view to move the camera toward or away from its center of interest. You can Ctrl + Alt + left-marquee a region to snap the center of interest to the center of that region.
Center of Interest is off by default.
If Center of Interest (and/or Local) and Bounding box are on, and you are currently in a four panel view, then when you middle-drag in any of the views, a red line with a small x at the end appears to indicate the Center of Interest.
Turning off this option dollies towards the current location of the Dolly Tool icon when you start dollying.
A box dolly moves the center of interest to the marquee region when you use Ctrl + Alt + drag (or Control + Option + drag on Mac OS X) to dolly the camera.
If on, when you perform a box dolly (Ctrl + drag) on an object, the center of interest moves onto the surface of the object. Calculating the surface point is slower if Smooth Shade mode is off (and especially if there are many visible objects in the scene).
If on, when you perform a box dolly (Ctrl + drag) on an object, the center of interest moves to the center of the object’s bounding box. Bounding Box is on by default.