Lens hood

In photography, a lens hood or lens shade is a device used on the front end of a lens to block the Sun or other light source(s) to prevent glare and lens flare. Lens hoods may also be used to protect the lens from scratches and the elements without having to put on a lens cover.The geometry of a lens hood is dependent on three parameters: the focal length of the lens, the size of the front lens element and the dimensions of the image sensor or film in the camera.The 'box' or 'cut-out' type lens hood of a Pentax DA 21 mm f/3.2 Limited lens.A conical chopped petal lens hood. Note that from this angle no part of the glass lens surface is visible, as the line of sight is blocked by the lens hood. (Canon EF 70–200 mm f/2.8).Lens without and with a conical chopped petal (or tulip) lens hood (Canon EF 28–105 mm f/3.5–4.5 USM II).Praktica camera – lens with a conical collapsible rubber lens hood (50 mm f/2.8). In photography, a lens hood or lens shade is a device used on the front end of a lens to block the Sun or other light source(s) to prevent glare and lens flare. Lens hoods may also be used to protect the lens from scratches and the elements without having to put on a lens cover.The geometry of a lens hood is dependent on three parameters: the focal length of the lens, the size of the front lens element and the dimensions of the image sensor or film in the camera. Flare occurs when stray light strikes the front element of a lens and then bounces around within the lens. This stray light often comes from very bright light sources, such as the Sun, bright studio lights, or a bright white background. If a light source is in the lens' angle of view, a lens hood will hardly have any effect, but the light does not have to cause lens flare. It is sufficient that stray light from a bright light source enters the lens. Multi-layer coatings in newer lenses also help to reduce lens flare. The shape of a lens hood can vary from a plain cylindrical or conical section (much like a lamp shade) to a more complex shape, sometimes called a petal, tulip, or flower hood. These more complex shapes take into account the final image's shape and aspect ratio. This allows the lens hood to block stray light with the longer portions of the lens hood, while allowing more light into the corners of the image through the shorter portions of the hood, thereby reducing the amount of mechanical vignetting (reduction of light around the periphery) in the final image.