The point of this exercise is to see how a zoom lens can be used in movies for suggesting depth to the audience.
As you can see I have taken three small ornaments and lined them up on white paper. Using a 55-300mm f/5.6 zoom lens, I zoomed in and focused on to the nearest object and locked the focus whilst angling the camera to include the other objects in the shot and maintaining a clean background. Then I filmed whilst I zoomed out and back in and not re-touching the focus. As you can see from the film as I zoom out the object in the background start to sharpen as they began to fall in to the field-of-focus and blur as I zoom back in.
I find the downside of zooming is that it is difficult to maintain a steady camera even when mounted to a tripod and that the zoom lenses that I have of my DSLR are not really designed for movie making and therefore are not easy to operate smoothly. They are also heavier than prime-lenses and are slower offering less versatility for lighting conditions.