Daniel Gies provides an overview for different techniques and methods for creating an automated camera focus system in After Effects that will allow you to easily focus on different objects in After Effects Layers easily.
I try to quickly explain a couple methods for tracking the cameras focus to moving objects or parented layers
Automating things like Camera Focus in After Effects can be a real time saver in comparison to setting keyframes for focus, which is a laborious task in and layer-heavy composition.
Daniel looks at two methods for tracking the focus of a moving object in After Effects, and discusses the advantages and disadvantages of both methods. Daniel shows how to create both methods for automatic focus using Expressions in After Effects, and shows how to set up the expressions near the end of the tutorial.