This week we tried to explain how the Mirage (an optical curiosity created by OPTI-GONE International) works to produce a 3-D image that appears to be floating out of a cut-out hole. The Mirage is made of two identical concave (and parabolic) mirrors with a circular hole in the top mirror. The focal point of each mirror is at the the vertex of the other mirror. Supposing that a flat, point object were to be placed at the focal point of the top mirror, on the bottom mirror, then any light coming from or reflecting off the object to the top mirror would travel as if from the focal point to the mirror and reflect parallel to the principal axis. This means that the light coming to the bottom mirror will be parallel to its principal axis (the same axis as the top mirror as these are identical mirrors), so the light will then reflect toward the bottom mirror’s focal point, which is at the hole in the top mirror. This produces a real image that you can see at the opening if you’re close enough to it.