A tube or shade that fits on the front of a lens. It blocks stray light from outside the picture area, such as direct sunlight coming from the side. This helps prevent flare and loss of contrast. A hood also protects the front of the lens from knocks and rain. Each hood is designed for a certain lens or focal length. A hood that is too long or narrow for the lens will cut off the corners of the picture, a problem called vignetting.
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