• A divergent laser beam passing through an iris diaphragm forms a dark spot in the middle when the iris is stopped down.
  • Can be projected on to a screen or whiteboard in a dark room.
  • The spot will be visible from ~1/2 m and beyond.

  • View seen by students in darkened room.

        (put laser at end of optics bench, front end should be at ~380 mm)
        (make divergent beam with 18 mm lens at 440 mm, .04 or .08 mm aperture at 458 mm, 252 mm lens at ~510 mm)
        (fine tune position of aperture using index card in front of 252 mm lens)
        (put iris diaphragm at ~550 mm, clamp with binder clip if it must be elevated)