, backscatter (also called near-camera reflection
) is an optical phenomenon
resulting in typically circular artifact
s on an image, due to the camera's flash
being reflected from unfocused
motes of dust
, water droplets
, or other particle
s in the air
or water. It is especially common with modern compact and ultra-compact digital cameras
Caused by the backscatter
of light by unfocused particles, these artifacts are also sometimes called orbs, referring to a common paranormal
claim. Some appear with trails, suggesting motion
Backscatter commonly occurs in low-light scenes when the camera's flash
is used. Cases include nighttime
and underwater photography
, when a bright light source and reflective unfocused particles are near the camera.
Light appears much brighter very near the source due to the inverse-square law
, which says light intensity is inversely proportional to the square of the distance from the source.
[Richard Ferncase. ]
Basic Lighting Worktext for Film and Video
'. CRC Press; 22 April 1992. . p. 66.
The artifact can result from the backscatter
of the light from airborne
solid particles, such as dust
, or liquid droplets, especially rain
. They can also be caused by foreign material within the camera lens.
The image artifacts usually appear as either white or semi-transparent
circles, though may also occur with whole or partial color spectra, purple fringing
or other chromatic aberration
. With rain droplets, an image may capture light passing through the droplet creating a small rainbow effect
[J. David Pye. ]
Polarised Light in Science and Nature
'. CRC Press; 6 May 2015. . p. 81.
describes the artifacts as a common photographic problem:
In underwater scenes, particles such as sand or plankton
ic marine life
near the lens, invisible to the diver, reflect light from the flash causing the orb artifact in the image. A strobe flash, which distances the flash from the lens, eliminates the artifacts.
[Nick Robertson-Brown. ]
Underwater Photography: Art and Techniques
'. Crowood; 31 January 2014. . p. 105.
The effect is also seen on infrared video cameras, where superbright infrared LEDs illuminate microscopic
particles very close to the lens. The artifacts are especially common with compact or ultra-compact cameras, where the short distance between the lens and the built-in flash decreases the angle
of light reflection
toward the lens, ''directly'' illuminating the aspect of the particles facing the lens and increasing the camera's ability to capture the light reflected from normally subvisible particles.
250px|A single orb in the center of the photo, at the person's knee level
Some ghost hunters
have claimed that orb shaped visual artifacts appearing in photographs are spirits of the dead.
Others have claimed that orbs are an unknown sort of being, based partly on perceived intent in the orbs' movements. Such perceptions have been interpreted by Michael Shermer
as examples of agenticity
. Prominent paranormal investigators such as Joe Nickell
have agreed with skeptic-debunkers' assessments that orbs result from natural phenomena like insects, dust, pollen, or water droplets.
[Joe Nickell.. p. 159.]
* Digital artifact
* Entoptic phenomenon
* Lens flare
* Rod (optical phenomenon)
* Rolling shutter
Category:Science of photography