Step 4: You'll see that the changes to focal length gives the illusion that the camera is moving backwards. To counteract this, you compensate by moving the camera forward.
Create a Position track for the camera. Leave the camera in its current position for frame 0, then move the timeline to the last frame of the animation and adjust the camera position so that the scene is captured with our new focal length as shown. Don't forget to record a keyframe for that last position.
And, that's all there is to it!