A pull- (or rack-) focus shot is more natural than you might think, so it's surprising that the shot is not used more in 3D animation. If you're standing on a street corner having a conversation with two other people, your eye cannot focus on all that is happening around your field of vision. Your eye can either focus on something close-up or far away. To look from one to the other, your eye refocuses; this is exactly what the camera does in a pull-focus shot.
Camera lenses can't focus on everything in a scene at once, and their focus needs to change to follow the action. In the computer environment, everything is always in focus. This is a good thing for the novice, as it is one less thing to worry about. For the professional, this is yet another element you need to be aware of and take action upon. One of the subtle differences between professional and amateur animations is the use of pull-focus shots and depth of fieldmaking the computer's eye work like a human eye. Although full shots and close-ups are more commonplace, mechanical and pull-focus shots allow you to take the viewer to a new perspective. As a digital director, you need to be aware of this and use pull-focus shots when appropriate. Figures 15 and 16 show the start and end of a pull-focus shot.
Figure 15 In this shot, the camera is fixed but focused on the character in the backdrop. Your eye is drawn to that character.
Figure 16 When the pull-focus is applied, a shift in the view brings your attention to the character in the foreground.