Lens flare
Encyclopedia
Lens flare is the light scattered in lens
systems through generally unwanted image formation mechanisms, such as internal reflection
and scattering
from material inhomogeneities in the lens. These mechanisms differ from the intended image formation mechanism that depends on refraction of the image rays. Flare manifests itself in two ways: firstly as a haze across the image, making the image look "washed out" by reducing contrast and color saturation (adding light to dark image regions, and adding white to saturated regions, reducing their saturation), and secondly as visible artifacts.
Flare is particularly caused by a very bright light sources either in the image – which produces visible artifacts – or shining into the lens but not in the image – which produces a haze. Most commonly, this occurs when shooting into the sun (when the sun is in frame or the lens is pointed in the direction of the sun), and is reduced by using a lens hood
or other shade.
For good optical systems and most images (which do not have a bright light shining into the lens), flare is a secondary effect that is widely distributed across the image and thus not visible, though it reduces contrast. Lenses with large numbers of elements such as zooms
tend to exhibit greater lens flare, as they contain multiple surfaces at which unwanted internal scattering occurs.
of the image formation elements. For example, if the lens has a 6-bladed aperture, the flare may have a hexagonal pattern.
Such internal scattering is also present in the human eye, and manifests in an unwanted veiling glare
most obvious when viewing very bright lights or highly reflective surfaces. In some situations, eyelash
es can also create flare-like irregularities, although these are technically diffraction artifacts.
When a bright light source is shining on the lens but not in its field of view, lens flare appears as a haze that washes out the image and reduces contrast. This can be avoided by shading the lens (the purpose for which lens hood
s are designed). In a studio, a gobo
or set of barn doors can be attached to the lighting to keep it from shining on the camera. Modern lenses use lens coatings to reduce the amount of reflection and minimize flare.
When using an anamorphic lens, as is common in analog cinematography, lens flare can manifest itself as a horizontal lines. This is most commonly seen in car headlights in a dark scene, and may be desired as part of the "film look".
For both of these reasons (implying realism and/or drama) artificial lens flare is a common effect in various graphics editing programs, although its use can be a point of contention among professional graphic design
ers. Lens flare was one of the first special effects developed for computer graphics
because it can be imitated using relatively simple means. Basic flare-like effects, for instance in computer and video games, can be obtained using static or animated starburst, ring, and disc texture
s that are moved according to the position of the light source. More sophisticated rendering techniques have been developed based on ray tracing
or photon mapping
.
Lens flare was typically avoided by Hollywood cinematographers, but when filming Easy Rider
, Laszlo Kovacs
was forced to jury-rig a camera car for his Arriflex, which resulted in numerous lens flares as he shot motorcycle footage against Southwestern U.S. landscapes.
JJ Abrams, the director of the 2009 version of Star Trek, used this technique. "I wanted a visual system that felt unique. I know there are certain shots where even I watch and think, "Oh that's ridiculous, that was too many." But I love the idea that the future was so bright it couldn't be contained in the frame."
David Boyd
, the director of photography of the sci-fi Firefly
series, desired this style so much (harking back to 1970s television), that he sent back the cutting-edge lenses which reduced lens flare in exchange for cheaper ones.
s can cause flare, particularly ghosts of bright lights (under central inversion). This can be eliminated by not using a filter, and reduced by using higher-quality filters or narrower aperture.
, which acts like a diffraction grating
. Unlike true lens flare, this artifact is not visible in the eyepiece of a digital SLR camera, making it more difficult to avoid.
Lens (optics)
A lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens consists of a single optical element...
systems through generally unwanted image formation mechanisms, such as internal reflection
Reflection (physics)
Reflection is the change in direction of a wavefront at an interface between two differentmedia so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves...
and scattering
Scattering
Scattering is a general physical process where some forms of radiation, such as light, sound, or moving particles, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which they pass. In conventional use, this also includes deviation of...
from material inhomogeneities in the lens. These mechanisms differ from the intended image formation mechanism that depends on refraction of the image rays. Flare manifests itself in two ways: firstly as a haze across the image, making the image look "washed out" by reducing contrast and color saturation (adding light to dark image regions, and adding white to saturated regions, reducing their saturation), and secondly as visible artifacts.
Flare is particularly caused by a very bright light sources either in the image – which produces visible artifacts – or shining into the lens but not in the image – which produces a haze. Most commonly, this occurs when shooting into the sun (when the sun is in frame or the lens is pointed in the direction of the sun), and is reduced by using a lens hood
Lens hood
In photography, a lens hood or lens shade is a device used on the end of a lens to block the sun or other light source in order to prevent glare and lens flare....
or other shade.
For good optical systems and most images (which do not have a bright light shining into the lens), flare is a secondary effect that is widely distributed across the image and thus not visible, though it reduces contrast. Lenses with large numbers of elements such as zooms
Zoom lens
A zoom lens is a mechanical assembly of lens elements for which the focal length can be varied, as opposed to a fixed focal length lens...
tend to exhibit greater lens flare, as they contain multiple surfaces at which unwanted internal scattering occurs.
Manifestation
The spatial distribution of the lens flare typically manifests as several starbursts, rings, or circles in a row across the image or view. Lens flare patterns typically spread widely across the scene and change location with the camera's movement relative to light sources, tracking with the light position and fading as the camera points away from the bright light until it causes no flare at all. The specific spatial distribution of the flare depends on the shape of the apertureAperture
In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are,...
of the image formation elements. For example, if the lens has a 6-bladed aperture, the flare may have a hexagonal pattern.
Such internal scattering is also present in the human eye, and manifests in an unwanted veiling glare
Glare (vision)
Glare is difficulty seeing in the presence of bright light such as direct or reflected sunlight or artificial light such as car headlamps at night. Because of this, some cars include mirrors with automatic anti-glare functions....
most obvious when viewing very bright lights or highly reflective surfaces. In some situations, eyelash
Eyelash
An eyelash or simply lash is one of the hairs that grow at the edge of the eyelid. Eyelashes protect the eye from debris and perform some of the same function as whiskers do on a cat or a mouse in the sense that they are sensitive to being touched, thus providing a warning that an object is near...
es can also create flare-like irregularities, although these are technically diffraction artifacts.
When a bright light source is shining on the lens but not in its field of view, lens flare appears as a haze that washes out the image and reduces contrast. This can be avoided by shading the lens (the purpose for which lens hood
Lens hood
In photography, a lens hood or lens shade is a device used on the end of a lens to block the sun or other light source in order to prevent glare and lens flare....
s are designed). In a studio, a gobo
Gobo (lighting)
A gobo derived from "Go Between" or Goes Before Optics -originally used on film sets, is a physical template slotted inside, or placed in front of, a lighting source, used to control the shape of emitted light....
or set of barn doors can be attached to the lighting to keep it from shining on the camera. Modern lenses use lens coatings to reduce the amount of reflection and minimize flare.
When using an anamorphic lens, as is common in analog cinematography, lens flare can manifest itself as a horizontal lines. This is most commonly seen in car headlights in a dark scene, and may be desired as part of the "film look".
Deliberate use
A lens flare is often deliberately used to invoke a sense of drama. A lens flare is also useful when added to an artificial or modified image composition because it adds a sense of realism, implying that the image is an un-edited original photograph of a "real life" scene.For both of these reasons (implying realism and/or drama) artificial lens flare is a common effect in various graphics editing programs, although its use can be a point of contention among professional graphic design
Graphic design
Graphic design is a creative process – most often involving a client and a designer and usually completed in conjunction with producers of form – undertaken in order to convey a specific message to a targeted audience...
ers. Lens flare was one of the first special effects developed for computer graphics
Computer graphics
Computer graphics are graphics created using computers and, more generally, the representation and manipulation of image data by a computer with help from specialized software and hardware....
because it can be imitated using relatively simple means. Basic flare-like effects, for instance in computer and video games, can be obtained using static or animated starburst, ring, and disc texture
Texture
Texture may refer to:* Textures , album of Brian Eno* Textures , a metal band from the Netherlands* Texture , theoretical topological defect in the structure of spacetime...
s that are moved according to the position of the light source. More sophisticated rendering techniques have been developed based on ray tracing
Ray tracing
In computer graphics, ray tracing is a technique for generating an image by tracing the path of light through pixels in an image plane and simulating the effects of its encounters with virtual objects. The technique is capable of producing a very high degree of visual realism, usually higher than...
or photon mapping
Photon mapping
In computer graphics, photon mapping is a two-pass global illumination algorithm developed by Henrik Wann Jensen that solves the rendering equation. Rays from the light source and rays from the camera are traced independently until some termination criterion is met, then they are connected in a...
.
Lens flare was typically avoided by Hollywood cinematographers, but when filming Easy Rider
Easy Rider
Easy Rider is a 1969 American road movie written by Peter Fonda, Dennis Hopper, and Terry Southern, produced by Fonda and directed by Hopper. It tells the story of two bikers who travel through the American Southwest and South with the aim of achieving freedom...
, Laszlo Kovacs
László Kovács (cinematographer)
László Kovács, A.S.C. was a Hungarian cinematographer who was influential in the development of American New Wave films. Most famous for his award-winning work on Easy Rider and Five Easy Pieces, Kovács was the recipient of numerous awards, including three Lifetime Achievement Awards...
was forced to jury-rig a camera car for his Arriflex, which resulted in numerous lens flares as he shot motorcycle footage against Southwestern U.S. landscapes.
JJ Abrams, the director of the 2009 version of Star Trek, used this technique. "I wanted a visual system that felt unique. I know there are certain shots where even I watch and think, "Oh that's ridiculous, that was too many." But I love the idea that the future was so bright it couldn't be contained in the frame."
David Boyd
David Boyd (cinematographer)
David R. Boyd A.S.C. is an American cinematographer, television director and camera operator best known for his role as director of photography for the FOX television series Firefly. He also worked as cinematographer on the first three episodes of HBO's Deadwood...
, the director of photography of the sci-fi Firefly
Firefly (TV series)
Firefly is an American space western television series created by writer and director Joss Whedon, under his Mutant Enemy Productions label. Whedon served as executive producer, along with Tim Minear....
series, desired this style so much (harking back to 1970s television), that he sent back the cutting-edge lenses which reduced lens flare in exchange for cheaper ones.
Filter flare
The use of photographic filterPhotographic filter
In photography and videography, a filter is a camera accessory consisting of an optical filter that can be inserted in the optical path. The filter can be a square or oblong shape mounted in a holder accessory, or, more commonly, a glass or plastic disk with a metal or plastic ring frame, which...
s can cause flare, particularly ghosts of bright lights (under central inversion). This can be eliminated by not using a filter, and reduced by using higher-quality filters or narrower aperture.
Diffraction artifact in digital cameras
One form of flare is specific to digital cameras. With the sun shining on an unprotected lens, a group of small rainbows appears. This artifact is formed by internal diffraction on the image sensorImage sensor
An image sensor is a device that converts an optical image into an electronic signal. It is used mostly in digital cameras and other imaging devices...
, which acts like a diffraction grating
Diffraction grating
In optics, a diffraction grating is an optical component with a periodic structure, which splits and diffracts light into several beams travelling in different directions. The directions of these beams depend on the spacing of the grating and the wavelength of the light so that the grating acts as...
. Unlike true lens flare, this artifact is not visible in the eyepiece of a digital SLR camera, making it more difficult to avoid.
See also
- BokehBokehIn photography, bokeh is the blur, or the aesthetic quality of the blur, in out-of-focus areas of an image, or "the way the lens renders out-of-focus points of light."...
, a source of circles around out-of-focus bright points, also due in part to the internals of the lens. - Diffraction spikeDiffraction spikeDiffraction spikes are lines radiating from bright light sources in reflecting telescope images. They are artifacts caused by light diffracting around the support vanes of the secondary mirror...
, a type of lens flare seen in some telescopeTelescopeA telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
s - Anti-reflective coatingAnti-reflective coatingAn antireflective or anti-reflection coating is a type of optical coating applied to the surface of lenses and other optical devices to reduce reflection. This improves the efficiency of the system since less light is lost. In complex systems such as a telescope, the reduction in reflections also...
, used to reduce lens flare and produces the red and green colors common in lens flare.