Turn ON depth of field for your camera to enable.
View your comp in the TOP view.
select the camera and you should see a plane for the focal point.
(scrub "Focal Distance" value and you can see which plane this is)
A layer is in perfect focus if its position minus the camera's position is equal to the Focus Distance value.
The formula reads as such -
You can take advantage of this formula to ensure that a layer is in focus by linking the camera's Focus Distance to a layer's position regardless of where the layer is positioned (static or animating).
For example, say you have a layer, let's call it HeroLayer, that you always want to be in focus. You would apply the following Expression to the Focus Distance property.
Now if you move either the camera or the heroLayer, the layer will always be in focus. You can also create a Null Layer that will allow you to easily change the 'perfect focus' from one layer onto another.
AE Training in South East Asia. AE templates for sale and rental. Click here for more