Dust reduction system
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System camera
A system camera is a camera with interchangeable components that constitutes the core of a system. Early representatives include Leica I Schraubgewinde , Exakta and the Nikon F...
s (often referred to in English as DSLRs or digital single-lens reflex camera
Digital single-lens reflex camera
Most digital single-lens reflex cameras are digital cameras that use a mechanical mirror system and pentaprism to direct light from the lens to an optical viewfinder on the back of the camera....
s) to solve the problem of dust
Dust
Dust consists of particles in the atmosphere that arise from various sources such as soil dust lifted up by wind , volcanic eruptions, and pollution...
particles adhering
Adhesion
Adhesion is any attraction process between dissimilar molecular species that can potentially bring them in close contact. By contrast, cohesion takes place between similar molecules....
to the image sensor
Image 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...
. Some systems remove or clean the sensor by vibrating at a very high frequency—between 100hertz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
and 50kilohertz. This is needed because every time lenses
Photographic lens
A camera lens is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image chemically or electronically.While in principle a simple convex lens will suffice, in...
are changed there is a chance that dust may enter the camera body and settle on the image sensor. Even if utmost care is taken when changing lenses, the mechanical parts such as shutter
Shutter (photography)
In photography, a shutter is a device that allows light to pass for a determined period of time, for the purpose of exposing photographic film or a light-sensitive electronic sensor to light to capture a permanent image of a scene...
or quick-return mirror might still generate dust contamination due to friction occurring during their movement. At the same time, these parts create movement of the air inside the camera body which is enough to whirl the minuscule dust particles around.
Types of systems
Different manufactures employ their own version of dust abatement. Currently there seem to be two main types of dust removal. One type uses a piezo crystalPiezoelectricity
Piezoelectricity is the charge which accumulates in certain solid materials in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure...
to vibrate a filter which covers the sensor. The second type moves the actual sensor—this may be supplemented by a controlled flow of air.
Piezo crystal ultrasonic vibration of filter
This shakes or vibrates the thin filter surface that covers 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...
many tens of thousands of times per second (35,000 to 50,000 hertz). This helps to clean and remove particles from the filter. Olympus devised a such a system, which Leica and Panasonic use it under license, they refer to as a "Supersonic Wave Filter
Supersonic Wave Filter
The Supersonic Wave Filter is a dust reduction system developed by Olympus to overcome the negative effect of dust particles landing on the image sensor of digital SLRs. DSLRs are particularly vulnerable to this issue, since the interior of the camera is exposed during lens changes unlike other...
". Canon also uses this type of system. Nikon uses this type of system, the refer the filter as low-pass
Low-pass filter
A low-pass filter is an electronic filter that passes low-frequency signals but attenuates signals with frequencies higher than the cutoff frequency. The actual amount of attenuation for each frequency varies from filter to filter. It is sometimes called a high-cut filter, or treble cut filter...
and the vibration series as high resonance
Resonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
.
Sensor shifting
This type of systems moves the actual sensor to help reduce dust. It vibrates the actual sensor at around 100 Hz. The amount of movement or sensor travel is larger that the higher frequency filter vibrating types.A crude analogy to compare it to the piezo crystal filter method is something like hitting or banging the sensor to displace the contaminant, whereas the piezo vibrates a filter to make the particles fall off. The sensor may also utilize a negatively charged surface coating to reduce static and help repel negatively charged particles. Konica MinoltaKonica Minolta
is a Japanese manufacturer of office equipment, medical imaging, graphic imaging, optical devices, and measuring instruments. It is headquartered in the Marunouchi Center Building in Marunouchi, Chiyoda, Tokyo, with a Kansai office in Nishi-ku, Osaka, Osaka Prefecture...
is credited with being the original developer of this type of system. Sony and Pentax incorporate sensor shifting in their cameras with Dust Reduction Systems.
Need for use with digital cameras
These problems are not as critical with film SLRsSingle-lens reflex camera
A single-lens reflex camera is a camera that typically uses a semi-automatic moving mirror system that permits the photographer to see exactly what will be captured by the film or digital imaging system, as opposed to pre-SLR cameras where the view through the viewfinder could be significantly...
as the dust disappears as the film is wound on, but with DSLRs the image sensor always remains in the same place. Even with dust particles no bigger than 0.1 mm (100 micrometres) and invisible to the human eye, once they land on the image sensor's surface they can degrade the quality of all the images taken thereafter. Furthermore, it is usually a difficult task to remove the dust, often making it necessary to send the camera in for servicing.
Types of dust particles
There are two main types of dust that can potentially degrade image quality: Dust particles that adhere throughelectric force and dust particles that adhere through intermolecular force.
(1) Dust particles adhering through electrostatic charges
Most of the contamination to be found on the image sensor surface is caused by dust particles as small as just one micrometre (0.001 mm) adhering to it through electrical charges. The particles themselves carry a positive static electric charge, while the image sensor is negatively charged, which makes them attract each other. The same phenomenon can be observed on the surface of LCD
Liquid crystal display
A liquid crystal display is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals . LCs do not emit light directly....
and CRT
Cathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
monitor screens.
(2) Dust particles adhering through intermolecular force
Intermolecular force
Intermolecular forces are forces of attraction or repulsion which act between neighboring particles: atoms, molecules or ions. They are weak compared to the intramolecular forces, the forces which keep a molecule together...
The intermolecular force is weaker than electrostatic charges. However, it still attracts microscopic-sized dust to the image sensor with infinitesimal force. While earthing (grounding) the camera can help reduce the problem of electrostatic dust it does not reduce intermolecular attraction. If, for example, flour were drizzled into the camera, it would still adhere to the surface of earthed metal. This kind of dust is attracted by intermolecular force. Liquid also adheres to the image sensor by intermolecular force and such molecules adhere strongly due to their ability to get closer to the adhesion surface, making it harder for dust reduction systems to remove these type of contaminants completely. In such instances, wiping the optical elements in front of the image sensor with cleaning fluid may be necessary.
History of dust reduction systems
OlympusOlympus Corporation
is a Japan-based manufacturer of optics and reprography products. Olympus was established on 12 October 1919, initially specializing in microscope and thermometer businesses. Its global headquarters are in Shinjuku, Tokyo, Japan, while its USA operations are based in Center Valley, Pennsylvania,...
was the first to include a dust reduction system on a DSLR, featuring their Supersonic Wave Filter
Supersonic Wave Filter
The Supersonic Wave Filter is a dust reduction system developed by Olympus to overcome the negative effect of dust particles landing on the image sensor of digital SLRs. DSLRs are particularly vulnerable to this issue, since the interior of the camera is exposed during lens changes unlike other...
(SSWF) dust reduction technology on the Olympus E-1
Olympus E-1
The Olympus E-1, introduced in 2003, was the first DSLR system camera designed from the ground up for digital photography. This contrasts with its contemporaries which offered systems based on reused parts from previous 135 film systems, modified to fit with a sensor size of APS-C.-Features:The E-1...
in 2003. All Olympus DSLRs with removable lenses have included this system, as have Panasonic
Panasonic
Panasonic is an international brand name for Japanese electric products manufacturer Panasonic Corporation, which was formerly known as Matsushita Electric Industrial Co., Ltd...
's and Leica's DSLRs; both companies use Olympus technology. Olympus Corporation was awarded an innovation prize by the Japan Institute of Invention and Innovation (JIII) in 2010 for its invention of automatic dust reduction for digital cameras.
Before that Sigma
Sigma Corporation
is a Japanese company founded in 1961, manufacturing cameras, lenses, flashes and other photographic accessories. All Sigma products are produced in the company's own Aizu factory in Bandai, Fukushima, Japan...
was sealing the mirror box of their cameras with a protective filter behind the lens mount, preventing dust from entering the camera body.
Other manufacturers, namely Sony
Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
(2006), Canon (2006), Pentax
Pentax
Pentax is a brand name used by Hoya Corporation for its medical-related products & services and Pentax Ricoh Imaging Company for cameras, sport optics , etc. Hoya purchased and merged with the Japanese optics company on March 31, 2008. Hoya's Pentax imaging business was sold to Ricoh Company, Ltd...
(2006), and Nikon
Nikon
, also known as just Nikon, is a multinational corporation headquartered in Tokyo, Japan, specializing in optics and imaging. Its products include cameras, binoculars, microscopes, measurement instruments, and the steppers used in the photolithography steps of semiconductor fabrication, of which...
(2007), followed suit with their own dust removal technologies. Each manufacturer uses a somewhat different system.
There have been several attempts by camera magazines to test the various dust reduction systems to see how effective they are. Pixinfo, Chasseur d’Images, and Camera Labs have all published their opinions, which can be summarized as saying that none of the systems are completely effective, but that the Olympus SSWF system is significantly better than most of the others, with the Nikon system perhaps a close second.
See also
- Ultrasonic cleaning
- ResonanceResonanceIn physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
- Low-pass filterLow-pass filterA low-pass filter is an electronic filter that passes low-frequency signals but attenuates signals with frequencies higher than the cutoff frequency. The actual amount of attenuation for each frequency varies from filter to filter. It is sometimes called a high-cut filter, or treble cut filter...