Editing Lens flare

{{short description|Image artifact that scattered or flared light within a lens system produces}}
[[File:Lens flare scheme en.svg|thumb|right|upright=1.5|Scheme of lens flare]]
[[File:Lens reflections on Sony SEL1855.JPG|thumb|Light coming from a narrow angle may be "[[Total internal reflection|trapped]]" and reflected between the surfaces of the lens elements.]]
[[File:A Lens flare.jpg|thumb|A lens flare]]

A '''lens flare''' happens when light is [[scattering|scattered]], or ''flared'', in a [[lens (optics)|lens]] system, often in response to a bright light, producing a sometimes undesirable [[artifact (error)|artifact]] in the image. This happens through light scattered by the imaging mechanism itself, for example through internal [[specular reflection|reflection]] and [[forward scatter]] from material imperfections in the lens. Lenses with large numbers of elements such as [[zoom lens|zooms]] tend to have more lens flare, as they contain a relatively large number of interfaces at which internal scattering may occur. These mechanisms differ from the focused image generation mechanism, which depends on rays from the refraction of light from the subject itself.

There are two types of flare: visible [[artifact (error)|artifacts]] and [[glare (vision)|glare]] across the image. The glare makes the image look "washed out" by reducing [[contrast (vision)|contrast]] and [[colorfulness|color saturation]] (adding light to dark image regions, and adding white to saturated regions, reducing their saturation). Visible artifacts, usually in the shape of the [[aperture]] made by the [[diaphragm (optics)|iris diaphragm]], are formed when light follows a [[optical path|pathway]] through the lens that contains one or more reflections from the lens surfaces.

Flare is particularly caused by very bright light sources. Most commonly, this occurs when aiming toward the [[Sun]] (when the Sun is in frame or the lens is pointed sunward), and is reduced by using a [[lens hood]] or other shade. For good-quality optical systems, and for 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, although it does reduce contrast.

== Manifestation ==
[[File:CCTV Lens flare.jpg|thumb|Severe flare in a [[Closed-circuit television|CCTV]] camera lens]]
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 [[aperture]] 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 (vision)|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 using a [[lens hood]]. In a studio, a [[Gobo (lighting)|gobo]] or set of [[barn doors]] can be attached to the lighting to keep it from shining on the camera. Filters can be attached to the camera lens which will also minimise lens flare, which is especially useful for outdoor photographers.

When using an [[anamorphic lens]], as is common in analog cinematography, lens flare can manifest itself as 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 ==
[[File:Lens Flare at Borobudur Stairs Kala Arches.JPG|thumb|right|upright|Lens flare on [[Borobudur]] stairs to enhance the sense of ascending]]

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]]ers.<ref name="adobe_photoshop_5_5_martin_evening_book">{{cite book |last= Evening |first= Martin |title= Adobe Photoshop 5.5 for Photographers: A professional image editor's guide to the creative use of Photoshop for the Macintosh and PC |url= https://books.google.com/books?id=bTkTgIjSd38C&pg=PA335 |page= 335 |publisher= [[Focal Press]] |date= March 2000 |isbn= 0-240-51591-9 |url-status= live |archive-url= https://web.archive.org/web/20171128142658/https://books.google.com/books?id=bTkTgIjSd38C&pg=PA335&lpg=PA335&dq=creative+use+of+lens+flare |archive-date= 2017-11-28 }}</ref> 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 [[video game|video games]], can be obtained by drawing starburst, ring, and disc [[Texture (visual arts)|textures]] over the image and moving them as the location of the light source changes.<ref name="essential_lightwave3d_lens_flare">{{cite book |last=Albee |first=Timothy |author2=Steve Warner |author3=Robin Wood |title=Essential lightwave 3D 8: the fastest and easiest way to master LightWave |url=https://books.google.com/books?id=eUp89F8nIbcC&pg=PA434 |page=434 |publisher=[[Wordwave Publishing]] |date=January 2005 |isbn=1-55622-082-0 |url-status=live |archive-url=https://web.archive.org/web/20171128142658/https://books.google.com/books?id=eUp89F8nIbcC&pg=PA434&dq=lens+flare#v=onepage&q=lens%20flare&f=false |archive-date=2017-11-28 }}</ref> More sophisticated rendering techniques have been developed based on [[ray tracing (graphics)|ray tracing]]<ref name="sig2011">{{cite journal |last= Hullin |first= Matthias |author2=Elmar Eisemann |author3=Hans-Peter Seidel |author4=Sungkil Lee|title=Physically based real-time lens flare rendering |journal= ACM Transactions on Graphics |volume= 30 |issue=4 |date=August 2011|pages= 1–10 |doi= 10.1145/2010324.1965003 }}</ref> or [[photon mapping]].<ref name="keshmirian-masters">{{cite book |last= Keshmirian |first= Arash |title=A physically-based approach for lens flare simulation |id=Master's Thesis Publication No. 1451802 |publisher= [[University of California, San Diego]] |date=August 2008}}</ref>

Lens flare was typically avoided by [[Cinema of the United States|Hollywood]] cinematographers, but the director [[J. J. Abrams]] deliberately added numerous lens flares to his films ''[[Star Trek (2009 film)|Star Trek]]'' (2009) and ''[[Super 8 (2011 film)|Super 8]]'' (2011) by aiming powerful off-camera light sources at the lens. He explained in an interview about ''Star Trek'': "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." Many complained of the frequent use; Abrams conceded it was "overdone, in some places."<ref>{{cite web |url=http://io9.com/5230278/jj-abrams-admits-star-trek-lens-flares-are-ridiculous |title=J.J. Abrams Admits Star Trek Lens Flares Are 'Ridiculous' |publisher=Io9.com |date=2009-04-27 |access-date=2012-12-06 |url-status=live |archive-url=https://web.archive.org/web/20121221114522/http://io9.com/5230278/jj-abrams-admits-star-trek-lens-flares-are-ridiculous |archive-date=2012-12-21 }}</ref> In contrast, the low-budget independent film ''[[Easy Rider]]'' (1969) contains numerous incidental lens flares that resulted from [[Harrison Arnold (cinematographer)|Harrison Arnold]]'s need to modify a [[camera car]] for his [[Arriflex]] as he shot motorcycle footage against landscapes of the [[Southwestern United States]].<ref>{{cite news | url=http://www.slate.com/id/2233176/entry/2233172/ | title=The Easy Rider Road Trip | author=Keith Phipps | work=[[Slate.com|Slate]] | date=2009-11-17 | access-date=2009-11-19 | url-status=live | archive-url=https://web.archive.org/web/20091120054432/http://www.slate.com/id/2233176/entry/2233172 | archive-date=2009-11-20 }}</ref>

[[David Boyd (cinematographer)|David Boyd]], the director of photography of the sci-fi ''[[Firefly (TV series)|Firefly]]'' series, desired this style's evocation of 1970s television so much that he sent back cutting-edge lenses that reduced lens flare in exchange for cheaper ones.<ref name="pilotcommentary">Whedon, ''Firefly: the complete series: "Serenity" commentary''</ref>{{check|date=November 2015}}

== Other forms of photographic flare ==

=== Filter flare ===
The use of [[photographic filter]]s can cause flare, particularly ghosts of bright lights (under [[central inversion]]).<ref>[http://toothwalker.org/optics/filterflare.html Filter Flare] {{webarchive|url=https://web.archive.org/web/20110321152942/http://toothwalker.org/optics/filterflare.html |date=2011-03-21 }}, Paul van Walree 2003–2010</ref> 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 sensor]], 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.

== Gallery ==
<gallery>
File:Lens Flare.jpg|Photograph of an [[Apollo Lunar Module]] containing lens flare. Besides the obvious flare around the [[Sun]], the light artifacts at the bottom right are also caused by flare.
File:Artificial lens flare.png|Sample of artificial lens flare, as might be used in an animated movie or video game
File:High-quality lens flare rendering.png|High-end lens flare rendering using a recent technique<ref>{{Cite web|url=https://resources.mpi-inf.mpg.de/lensflareRendering/|title=Physically-Based Real-Time Lens Flare Rendering}}</ref>
File:Edinburgh-Princesstreet2.jpg|Lens flare is extremely difficult to control when a bright light source like the Sun is just outside the frame.
File:Firework with lens flare.jpg|When the subject of a photo is the light source itself, lens flare can be a desirable and dramatic effect.
File:Solar eclipse Austria 2011 Jan 04.JPG|Lens flare used to capture details of too bright motive (partial [[solar eclipse]])
File:20100525 Imbros Marmaros Turkey example of Lens Flare.jpg|Lens flare - the Sun is outside the frame.
File:Mograph lensflare.png|Lens flare commonly associated with the use of [[Anamorphic format|anamorphic lenses]] which are often used in the production of films
File:Kensington Palace Gardens - London - UK.jpg|Lens flare example in picture of [[Kensington Gardens]] - [[London]], [[UK]]
File:Man playing guitar in a portrait with lens flare.jpg|alt=Lens flare example|Lens flare example in picture in a portrait. 50&nbsp;mm at f1.4
File:Antony Leung - Oresteia - Stairwell Theater, 2019.jpg|Lens flare over Anthony Leung using theatre lighting during Stairwell Theater's [[Oresteia]] - Brooklyn, NY, 2019
File:MarsPerseveranceRover-Rainbow-20210404.png|Many mistook an April 4, 2021 lens flare on Mars, which appears in a ''[[Perseverance (rover)|Perseverance]]'' rover photograph, for a rainbow, until NASA clarified the issue.<ref name="NASA-20210407">{{cite news |author=NASAPersevere |title=Twitter Tweet: Rainbow On Mars - No, A Lens Flare |url=https://twitter.com/NASAPersevere/status/1379536046338154498 |date=7 April 2021 |work=[[NASA]] |accessdate=8 April 2021 }}</ref><ref name="SPC-20210407">{{cite news |last=Wall |first=Mike |title=No, the Perseverance rover didn't spot a rainbow on Mars |url=https://www.space.com/perseverance-rover-mars-rainbow-photo |date=7 April 2021 |work=[[w:Space.com|Space.com]] |accessdate=8 April 2021 }}</ref>
File:Lens flare Bow River trail Calgary, Alberta.jpg|Lens flare in shadow of poplar tree
File:LensFlare.jpg|Extreme lens flare caused by intense sunlight
File:Optical Ground Station 2.webm|Lens flare in a film clip
File:'Perception of Christ Ascending to Heaven' Dome of the Rotunda of the church of the Holy Sepulchre Jerusalem Victor Grigas 2011 -1-19.jpg|Sensor flare - light is reflected off the sensor to the lens and then back to the sensor
</gallery>

== See also ==
* [[Anti-reflective coating]], used to reduce lens flare and produces the red and green colors common in lens flare.
* [[Bokeh]], a source of circles around out-of-focus bright points, also due in part to the internals of the lens.
* [[Diffraction spike]], a type of lens flare seen in some [[telescope]]s

== References ==
{{Reflist}}

{{Photography}}
{{Commons category|Lens flares}}

{{DEFAULTSORT:Lens Flare}}
[[Category:Image defects]]
[[Category:Lenses]]
[[Category:Optical phenomena]]