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The concave mirror is made with a surface that bends inward. Because the center of the curve is directed away from any incident light, it creates a reflection that is typically larger than the actual focal point.

This type of mirror is considered a converging device because it collects the light that falls into the bowl created by the inward bulge of the surface. This collection causes the light to refocus into a single focal length. The light is collected at different angles, since the concave nature of the bulge allows the light rays to make normal contact at differing depths at each point on the surface of the mirror.