Motion Path Camera
Say you need to create a scene where you have a camera that follows a motion path and holds focus on the subject until a given point in time and then leaves our subject to focus on another part of the scene. In this tutorial, a sphere will be our subject in the shot. We will use two locators as our “Home” and “Target” aim constraint for our camera.

1) Create your scene with the motion path for the camera and a two node camera.

2) Attach the camera to the motion path with "Follow" turned off. This will allow you to manipulate the aim node independently in your scene. Click here for an image.

3) Create two locators, one at the center of your subject (the sphere) named "Home", and one at the end of your camera motion path named "Target". Doing this will also allow you to animate the position of the "Target" locator and your camera will always remain focused on this locator. Click here for an image.

4) Select the two locators, and then shift-select the camera aim node.

5) In the Animation menu set, select "Constrain > Point". This should give you a new input node with a few options. Click here for an image.

6) In the "Camera_aim_pointConstraint" section, make sure the Node State is Normal and all the offsets are set to zero. Set the "Target" value to 0 and the "Home" value to 1. Set a keyframe for those two values at the first frame in your amimation. Click here for an image.

7) Move to a point in the animation where you want your camera to start pulling away from its target. Set another keyframe at that point with the same values as step 6 above. Click here for an image.

8) Move to a point in the animation where you want the camera to be completely off of your target and headed down its motion path. Change the two values in step 6 to "Home" = 0, "Target" = 1. Click here for an image.

9) Set a new keyframe for those values.

10) Open the Graph Editor and make sure the keyframes set at step 8 are “Linear Tangents”. Click here for an image.

Now when you playback your animation it will have the camera animation complete. Click here to see a playblast of the final results.