Technique for visualizing density variations in transparent media, usually air. Essentially exaggerates the effects of refraction in different densities of air caused by heat (hot air expands, cool air contracts) or pressure (like ultrasonic transducers). Effect can be observed using just a few low-cost components:

  1. Concave mirror with a long focal length (3-4ft or more) - spherical mirrors work best, but parabolic mirrors can work
  2. Point light source - the brightest, smallest light source you can find/make. Lasers don't work well, but a simple LED with a pinhole cover or a strand of fiber optic will work. Doesn't need to be very bright.
  3. Razor blade or color filter
  4. Camera

Diagram of typical setup:

Articles:

DIY projects:

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