Size of Image

DCS Code: 6A10.50 Last Updated: March 27, 2026
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Purpose

A masked plane mirror shows that a mirror only half the size of your face can display your complete reflection, regardless of viewing distance. Demonstrates the geometry of plane mirror image formation using similar triangles.

Paper mask with rectangular cutout mounted on a ring stand platform at head height, stabilized with a lead brick; a meter stick alongside provides scale
Figure 1: Masked mirror on an adjustable ring stand platform. The cutout is smaller than a face, yet viewers see their complete reflection regardless of distance.
Equipment