Limelight is a theatrical, mysterious environment in which viewers often feel as though they are witnessing a swirling nebula. Visitors stand on one side of a frosted screen and view projections of magnified grains of dust, pollen, and other particles floating in convection currents created by the heat of a spotlight placed on the opposite side of the screen. The appearance and size of the particles change as they float in and out of focus. When the particles are in focus, they possess color, shape, and form. When out-of-focus, they lose their hard-edge identity but retain their ability to absorb and reflect light. These out-of-focus particles are seen as circles of confusion (out-of-focus highlights).

Dust is everywhere in Tucson. Although we usually do not take time to notice, airborne dust is frequently visible in light rays both inside and out-of-doors. The dust in Limelight was gathered from air vents, floors, and other locations in the Center for Creative Photography.

Activities: Seeing dust

  1. Investigate where dust is visible in the classroom. For instance, can you see dust in the sunlight streaming through the window? Or, in a darkened room, can you see dust in the beam a flashlight or in the light of a slide or film projector?
  2. Explore depth of field, a concept that applies to both a camera and our human eyesight.
    1. Tell the students to hold their thumbs up about six inches from their eye.
    2. Tell them to focus on their thumb and notice that, while it is in focus, the rest of the room is out of focus. Then, tell them to look at the far wall beyond their thumb and to notice that when their eyes focus on something far away, they cannot also see their thumb in focus.
      Note: This is an example of depth of field. In photography, it refers to an area between the nearest and farthest points from the camera lens that are acceptably sharp in the focused image. The same concept holds true for our eyes, since they have lenses, too.


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