Description: A laser is shone onto a needlehead. When the shadow is viewed from far field concentric rings can be seen around the needlehead, and a bright spot will appear in the middle of the shadow.
Instructions: Setup on light track. Use a diverging lens to spread the beam out just enough that it barely encompasses the needlehead. Bring posterboard/paper close to the needlehead (from behind) and show the shadow. Take it further away to show the bright spot.
