As you watch the movie the stage is being lowered. Consequently, the bottom
of the crystal will come into focus first (movie slide at position 1).
At this position the smallest particles around the large one are also in
focus. The top of the crystal is in focus at position 2. At the end of
the movie dust particles from the coverslip come into focus. Use the selection
bar on the movie to go slowly through the different palnes of focus. Be
sure to hide the movie when you are finished.