PhysicsLAB: Demonstration: Real Images

Two concave mirrors are placed so that each front surface coincides with the focus of the other mirror.
When an object is placed on the inner surface of the bottom mirror, its image appears to "hover" inside the opening in the top mirror - at the focus of the bottom mirror. This illusion is a real image.
The illusion is formed by two concave mirrors of equal radius facing each other. The apex of the top mirror is at half of the radius from the bottom mirror and vice versa as shown in the figure on the right. When an object such as a small plastic toy house is hidden at the center of the bottom mirror one sees two images above near the apex of the top mirror. The ray diagram for this image has to be drawn with some care using rulers and protractors and applying the law of reflection.	Image courtesy of Tsing Bardin Physics Toys