Strictly speaking, vortex masks are not the only way to cancel the light from a star.

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The boss of Royal Bank of Scotland (RBS) should not have to cancel his bonus in light of the Libor rate-fixing scandal, its chairman has told MPs.

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They discovered that by shifting the "phase" of light so that the peaks of one wave line up with the valleys of an adjacent one, the two cancel each other, creating "shadows" between waves that are smaller than the waves themselves(see diagram, p. 141).

FORBES: Trick Of The Light

They discovered that, by shifting the "phase" of light so that the peaks of one wave line up with the valleys of an adjacent wave, the two waves cancel each other out, creating "shadows" between waves that are smaller than the waves themselves(see chart).

FORBES: Trick of the Light