Continuously refocusing camera

[Mike Clasby]

I think this might do what you want, it’s worth a try.

Click Dan Ebbert’s head and Scroll down to:

Building the World’s Greatest Cameraman
using After Effects 5.5’s Expression Controls

In the final comp, “Pan, Tilt and Focus & Zoom” , if you disable the random expressions for the target layer, Dan, Evol, James and Larry, then spread them out on the Z, then if you animate the camera’s position (Camera 1), you get what you want… methinks. The layers focused on are controlled by Slider Control in the Null 1 layer. So by keyframing the correct layer order number, you get the camera to focus in the order you want.

[Colin Braley]

Something like this should do the trick, as long as none of your layers are parented to anythiing. Just create a null named “Controls” and add a slider called “layer index” Then keyframe “layer index” as the number of the layer you want to focus on. Then add the expression below to the focus distance property of your camera.

layerIndexSwitch =thisComp.layer(“Controls”).effect(“layer index”)(“Slider”);
nearestKey = layerIndexSwitch.nearestKey( time );
nextKey = layerIndexSwitch.key( nearestKey.index );
distanceOne = length( position – thisComp.layer( nearestKey.value ).position );
distanceTwo = length( position – thisComp.layer( nextKey.value ).position );
ease( time, nearestKey.time, nextKey.time, distanceOne, distanceTwo )

I wrote this one really quick and didnt test it much so let me know if you have any problems.
~Colin