photography Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is emplo ...

, a lens hood or lens shade is a device used on the front end of a

lens A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements ...

to block the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

or other

light source Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 terah ...

(s) to prevent

glare Glare (derived from GLAss REinforced laminate ) is a fiber metal laminate (FML) composed of several very thin layers of metal (usually aluminum) interspersed with layers of S-2 glass-fiber ''pre-preg'', bonded together with a matrix such as epo ...

and

lens flare A lens flare happens when light is scattered or flared in a lens system, often in response to a bright light, producing a sometimes undesirable artifact in the image. This happens through light scattered by the imaging mechanism itself, for ex ...

. Lens hoods may also be used to protect the lens from scratches and the elements without having to put on a

lens cover A lens cover or lens cap provides protection from scratches and minor collisions for camera and camcorder lenses. Lens covers come standard with most cameras and lenses. Some mobile camera phones include lens covers, such as the Sony Ericsson ...

.
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.

Cause of lens flare

Flare occurs when

stray light Stray light is light in an optical system, which was not intended in the design. The light may be from the intended source, but follow paths other than intended, or it may be from a source other than the intended source. This light will often set a ...

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 The angle of view is the decisive variable for the visual perception of the size or projection of the size of an object. Angle of view and perception of size The perceived size of an object depends on the size of the image projected onto the ...

, 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 A coating is a covering that is applied to the surface of an object, usually referred to as the substrate. The purpose of applying the coating may be decorative, functional, or both. Coatings may be applied as liquids, gases or solids e.g. Powd ...

in newer lenses also help to reduce lens flare.

Types

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 In photography and optics, vignetting is a reduction of an image's brightness or saturation toward the periphery compared to the image center. The word '' vignette'', from the same root as ''vine'', originally referred to a decorative bord ...

(reduction of light around the periphery) in the final image. The geometry of a lens hood is dependent on three things: * focal length of the lens, * size of the front lens element, * dimensions of the image sensor or film in the camera. Ideally, lens hoods should increase in length, and therefore in efficiency, as the focal length of the lens increases and the angle of view reduces. Lens hoods are more prominent in

long focus lens In photography, a long-focus lens is a camera lens which has a focal length that is longer than the diagonal measure of the film or sensor that receives its image. It is used to make distant objects appear magnified with magnification increas ...

es because they have a smaller viewing angle than that of

wide-angle lens In photography and cinematography, a wide-angle lens refers to a lens whose focal length is substantially smaller than the focal length of a normal lens for a given film plane. This type of lens allows more of the scene to be included in the ...

es. For wide angle lenses, the length of the hood (away from the end of the lens) cannot be as long as those for telephoto lenses, as a longer hood would enter the wider field of view of the lens. Maximum aperture also affects the shape of a lens hood. As the aperture gets larger the amount of light and consequently the amount of the frame the sensor "sees" increases. This can be seen when comparing two lens hoods of the same focal length but with differing apertures – compare the lens hood of a telephoto 4 lens with that of the same lens but with a maximum aperture of 2.8. Correctly made rectangular or square lens hoods are generally more efficient than cylindrical or conical ones because those shapes closely resemble the shape of the photograph. However, rectangular or square lens hoods should not be used with zoom lenses whose front elements rotate as the

focal length The focal length of an optical system is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power. A positive focal length indicates that a system converges light, while a negative foc ...

is changed, as the hood will rotate as well, blocking parts of the angle of view. The same also applies to petal lens hoods. For these types of lenses, only cylindrical or conical lens hoods will work effectively. In addition, lens hoods can offer some degree of physical protection for the lens due to the hood extending farther than the lens itself.Harmer, Jim
"What does a lens hood do?"
''Improve Photography'', 15 Jun 2011 File:Pentax K-5 4773 06.jpg, The "box" or "cut-out" type lens hood of a Pentax DA 21 mm 3.2 Limited lens. File:Canon EF 70-200mm F2.8L lens with hood.jpg, 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 2.8). File:Canon EF 28-105 3.5-4.5 USM II with and without Lens Hood.jpg, Lens without and with a conical chopped petal (or tulip) lens hood (Canon EF 28–105 mm 3.5–4.5 USM II). File:Sonnenblende.jpg , Praktica camera – lens with a conical collapsible rubber lens hood (50 mm 2.8). Lens hoods with an extending bellows design (much like the

bellows A bellows or pair of bellows is a device constructed to furnish a strong blast of air. The simplest type consists of a flexible bag comprising a pair of rigid boards with handles joined by flexible leather sides enclosing an approximately airtig ...

of a medium or large format camera) can be adjusted for depth. This means that the depth can be increased when used on longer focal length lenses, and reduced as necessary for shorter focal length lenses.

Storage

Lens hoods that are supplied by the manufacturer of the lens are often designed to fit onto the matching lens facing either forward, for normal use, or backwards, so that the hood may be stored with the lens without occupying much additional space. Rubber lens hoods are flexible and generally collapse for storage. However other lens hoods must be removed if these features are not available and length extension of the lens is not preferred during storage.

References

External links

lenshoods.net
(»Free printable cardboard lens hoods«) {{Photography Photography equipment

Cause of lens flare

Types

Storage

See also

References

External links