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A peripheral is a device attached to a host computer but not part of it whose primary
functionality is dependent upon the host, and can therefore be considered as expanding
the host's capabilities, while not forming part of the system's core architecture.
Examples are printers, scanners, tape drives, microphones, speakers, webcams, and
cameras.
1: Printer (computing)
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A Lexmark printer
In computing, a printer is a peripheral which produces a hard copy (permanent readable
text and/or graphics) of documents stored in electronic form, usually on physical print
media such as paper or transparencies. Many printers are primarily used as local
peripherals, and are attached by a printer cable or, in most newer printers, a USB cable to
a computer which serves as a document source. Some printers, commonly known as
network printers, have built-in network interfaces (typically wireless and/or Ethernet),
and can serve as a hardcopy device for any user on the network. Individual printers are
often designed to support both local and network connected users at the same time. In
addition, a few modern printers can directly interface to electronic media such as memory
sticks or memory cards, or to image capture devices such as digital cameras, scanners;
some printers are combined with a scanners and/or fax machines in a single unit, and can
function as photocopiers. Printers that include non-printing features are sometimes called
Multifunction printers (MFP), Multi-Function Devices (MFD), or All-In-One (AIO)
printers. Most MFPs include printing, scanning, and copying among their features.
A Virtual printer is a piece of computer software whose user interface and API resemble
that of a printer driver, but which is not connected with a physical computer printer.
Printers are designed for low-volume, short-turnaround print jobs; requiring virtually no
setup time to achieve a hard copy of a given document. However, printers are generally
slow devices (30 pages per minute is considered fast; and many inexpensive consumer
printers are far slower than that), and the cost per page is actually relatively high.
However this is offset by the on-demand convenience and project management costs
being more controllable compared to an out-sourced solution. The printing press naturally
remains the machine of choice for high-volume, professional publishing. However, as
printers have improved in quality and performance, many jobs which used to be done by
professional print shops are now done by users on local printers; see desktop publishing.
The world's first computer printer was a 19th century mechanically driven apparatus
invented by Charles Babbage for his Difference Engine.[
2 : Image scanner
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Desktop scanner, with the lid raised. An object has been laid on the glass, ready for
scanning.
Scan of the jade rhinoceros seen in the photograph above.
Jump to: navigation, search
Image scanner.
In computing, a scanner is a device that optically scans images, printed text,
handwriting, or an object, and converts it to a digital image. Common examples found in
offices are variations of the desktop (or flatbed) scanner where the document is placed on
a glass window for scanning. Hand-held scanners, where the device is moved by hand,
have evolved from text scanning "wands" to 3D scanners used for industrial design,
reverse engineering, test and measurement, orthotics, gaming and other applications.
Mechanically driven scanners that move the document are typically used for large-format
documents, where a flatbed design would be impractical.
Modern scanners typically use a charge-coupled device (CCD) or a Contact Image Sensor
(CIS) as the image sensor, whereas older drum scanners use a photomultiplier tube as the
image sensor. A rotary scanner, used for high-speed document scanning, is another type
of drum scanner, using a CCD array instead of a photomultiplier. Other types of scanners
are planetary scanners, which take photographs of books and documents, and 3D
scanners, for producing three-dimensional models of objects.
Another category of scanner is digital camera scanners, which are based on the concept
of reprographic cameras. Due to increasing resolution and new features such as antishake, digital cameras have become an attractive alternative to regular scanners. While
still having disadvantages compared to traditional scanners (such as distortion,
reflections, shadows, low contrast), digital cameras offer advantages such as speed,
portability, gentle digitizing of thick documents without damaging the book spine. New
scanning technologies are combining 3D scanners with digital cameras to create fullcolor, photo-realistic 3D models of objects.
In the biomedical research area, detection devices for DNA microarrays are called
scanners as well. These scanners are high-resolution systems (up to 1 µm/ pixel), similar
to microscopes. The detection is done via CCD or a photomultiplier tube (PMT).
3 : Tape drive
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This article may require cleanup to meet Wikipedia's quality standards. Please
improve this article if you can. (July 2009)
DDS tape drive. Above, from left to right: DDS-4 tape (20 GB), 112m Data8 tape (2.5
GB), QIC DC-6250 tape (250 MB), and a 3.5" floppy disk (1.44 MB).
A tape drive, which is also known as a streamer, is a data storage device that reads and
writes data stored on a magnetic tape. It is typically used for archival storage of data
stored on hard drives. Tape media generally has a favorable unit cost and long archival
stability.
Instead of allowing random-access to data as hard disk drives do, tape drives only allow
for sequential-access of data. A hard disk drive can move its read/write heads to any
random part of the disk platters in a very short amount of time, but a tape drive must
spend a considerable amount of time winding tape between reels to read any one
particular piece of data. As a result, tape drives have very slow average seek times.
Despite the slow seek time, tape drives can stream data to tape very quickly. For
example, modern LTO drives can reach continuous data transfer rates of up to 80 MB/s,
which is as fast as most 10,000 rpm hard disks.
[edit] Media
Magnetic tape is commonly housed in a casing such as plastic known as a cassette or a
cartridge—for example, the 4-track cartridge and the compact cassette. The cassette
contains magnetic tape to provide different audio content using the same player. The
plastic outer shell permits ease of handling of the fragile tape, making it far more
convenient and robust than having loose or exposed tape.
[edit] History
Year Manufacturer
Model
Advancements
1951
Remington
Rand
UNISERVO First computer tape drive
1952 IBM
726
1958 IBM
729
1964 IBM
2400
1970s IBM
3400
1972 3M
QIC-11
1974 IBM
3850
1980 Cipher
(F880?)
1984 IBM
3480
1984 DEC
1986 IBM
TK50
3480
Use of plastic tape (cellulose acetate); 7-track tape
recording 6-bit bytes
Separate read/write heads providing transparent readafter-write verification [2]. [2]
9-track tape that could store every 8-bit byte plus a
parity bit.
Auto-loading tape reels and drives, avoiding manual
tape threading; Group code recording for error
recovery at 6250 bit-per-inch density
Tape cassette (with two reels)
Tape cartridge (with single reel)
First tape library with robotic access [3]
RAM buffer to mask start-stop delays [4] [5]
Internal takeup reel with automatic tape takeup
mechanism.
Thin-film magnetoresistive (MR) head. [6]
Linear serpentine recording [7]
Hardware data compression (IDRC algorithm) [8]
First helical digital tape drive.
1987 Exabyte/Sony EXB-8200
1993 DEC
Tx87
1995 IBM
3570
1996 HP
DDS3
1997 IBM
VTS
1999 Exabyte
Mammoth-2
Elimination of the capstan and pinch-roller system.
Tape directory (database with first tapemark nr on
each serpentine pass). [9]
Head assembly that follows pre-recorded tape servo
tracks (Time Based Servoing or TBS) [10]
Tape on unload rewound to the midpoint — halving
access time (requires two-reel cassette, resulting in
lesser capacity) [11]
Partial Response Maximum Likelihood (PRML)
reading method — no fixed thresholds[12]
Virtual tape — disk cache that emulates tape drive
[13]
The small cloth-covered wheel cleaning tape heads.
Inactive burnishing heads to prep the tape and deflect
any debris or excess lubricant.
Section of cleaning material at the beginning of each
data tape.
2000 Quantum
Super DLT
2003
2003
2006
2007
2008
3592
SAIT-1
T10000
3592
TS1130
IBM
Sony
StorageTek
IBM
IBM
optical servo allows more precise positioning of the
heads relative to the tape[14].
Virtual backhitch
Single-reel cartridge for helical recording
Multiple head assemblies and servos per drive [15]
Encryption capability integrated into the drive
GMR heads in a linear tape drive
4 : Microphone
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"Microphones" redirects here. For the Indie band, see The Microphones.
A microphone, colloquially called a mic or mike (both pronounced /ˈmaɪk/), is an
acoustic-to-electric transducer or sensor that converts sound into an electrical signal.
Microphones are used in many applications such as telephones, tape recorders, hearing
aids, motion picture production, live and recorded audio engineering, in radio and
television broadcasting and in computers for recording voice, VoIP, and for non-acoustic
purposes such as ultrasonic checking.
A Neumann U87 condenser microphone
The most common design today uses a thin membrane which vibrates in response to
sound pressure. This movement is subsequently translated into an electrical signal. Most
microphones in use today for audio use electromagnetic induction (dynamic
microphone), capacitance change (condenser microphone, pictured right), piezoelectric
generation, or light modulation to produce the signal from mechanical vibration.
[edit] Varieties
The sensitive transducer element of a microphone is called its element or capsule. A
complete microphone also includes a housing, some means of bringing the signal from
the element to other equipment, and often an electronic circuit to adapt the output of the
capsule to the equipment being driven. Microphones are referred to by their transducer
principle, such as condenser, dynamic, etc., and by their directional characteristics.
Sometimes other characteristics such as diaphragm size, intended use or orientation of the
principal sound input to the principal axis (end- or side-address) of the microphone are
used to describe the microphone.
[edit] Condenser, capacitor or electrostatic microphone
Inside the Oktava 319 condenser microphone
In a condenser microphone, also known as a capacitor or electrostatic microphone, the
diaphragm acts as one plate of a capacitor, and the vibrations produce changes in the
distance between the plates. There are two methods of extracting an audio output from
the transducer thus formed: DC-biased and radio frequency (RF) or high frequency (HF)
condenser microphones. With a DC-biased microphone, the plates are biased with a fixed
charge (Q). The voltage maintained across the capacitor plates changes with the
vibrations in the air, according to the capacitance equation (C = Q / V), where Q = charge
in coulombs, C = capacitance in farads and V = potential difference in volts. The
capacitance of the plates is inversely proportional to the distance between them for a
parallel-plate capacitor. (See capacitance for details.) The assembly of fixed and movable
plates is called an "element" or "capsule."
A nearly constant charge is maintained on the capacitor. As the capacitance changes, the
charge across the capacitor does change very slightly, but at audible frequencies it is
sensibly constant. The capacitance of the capsule (around 5–100 pF) and the value of the
bias resistor (100 megohms to tens of gigohms) form a filter which is highpass for the
audio signal, and lowpass for the bias voltage. Note that the time constant of an RC
circuit equals the product of the resistance and capacitance.
Within the time-frame of the capacitance change (as much as 50 ms at 20 Hz audio
signal), the charge is practically constant and the voltage across the capacitor changes
instantaneously to reflect the change in capacitance. The voltage across the capacitor
varies above and below the bias voltage. The voltage difference between the bias and the
capacitor is seen across the series resistor. The voltage across the resistor is amplified for
performance or recording.
AKG C451B small-diaphragm condenser microphone
RF condenser microphones use a comparatively low RF voltage, generated by a lownoise oscillator. The oscillator may either be amplitude modulated by the capacitance
changes produced by the sound waves moving the capsule diaphragm, or the capsule may
be part of a resonant circuit that modulates the frequency of the oscillator signal.
Demodulation yields a low-noise audio frequency signal with a very low source
impedance. The absence of a high bias voltage permits the use of a diaphragm with looser
tension, which may be used to achieve wider frequency response due to higher
compliance. The RF biasing process results in a lower electrical impedance capsule, a
useful byproduct of which is that RF condenser microphones can be operated in damp
weather conditions which could create problems in DC-biased microphones whose
insulating surfaces have become contaminated. The Sennheiser "MKH" series of
microphones use the RF biasing technique.
Condenser microphones span the range from telephone transmitters to inexpensive
karaoke microphones to high-fidelity recording microphones. They generally produce a
high-quality audio signal and are now the popular choice in laboratory and studio
recording applications. The inherent suitability of this technology is due to the very small
mass that must be moved by the incident sound wave, unlike other microphone types
which require the sound wave to do more work. They require a power source, provided
either via microphone outputs as phantom power or from a small battery. Power is
necessary for establishing the capacitor plate voltage, and is also needed to power the
microphone electronics (impedance conversion in the case of electret and DC-polarized
microphones, demodulation or detection in the case of RF/HF microphones). Condenser
microphones are also available with two diaphragms, the signals from which can be
electrically connected such as to provide a range of polar patterns (see below), such as
cardioid, omnidirectional and figure-eight. It is also possible to vary the pattern smoothly
with some microphones, for example the Røde NT2000 or CAD M179.
[edit] Electret condenser microphone
Main article: Electret microphone
First patent on foil electret microphone by G. M. Sessler et al. (pages 1 to 3)
An electret microphone is a relatively new type of capacitor microphone invented at Bell
laboratories in 1962 by Gerhard Sessler and Jim West.[1] The externally-applied charge
described above under condenser microphones is replaced by a permanent charge in an
electret material. An electret is a ferroelectric material that has been permanently
electrically charged or polarized. The name comes from electrostatic and magnet; a static
charge is embedded in an electret by alignment of the static charges in the material, much
the way a magnet is made by aligning the magnetic domains in a piece of iron.
Due to their good performance and ease of manufacture, hence low cost, the vast majority
of microphones made today are electret microphones; a semiconductor manufacturer[2]
estimates annual production at over one billion units. Nearly all cell-phone, computer,
PDA and headset microphones are electret types. They are used in many applications,
from high-quality recording and lavalier use to built-in microphones in small sound
recording devices and telephones. Though electret microphones were once considered
low quality, the best ones can now rival traditional condenser microphones in every
respect and can even offer the long-term stability and ultra-flat response needed for a
measurement microphone. Unlike other capacitor microphones, they require no
polarizing voltage, but often contain an integrated preamplifier which does require power
(often incorrectly called polarizing power or bias). This preamplifier is frequently
phantom powered in sound reinforcement and studio applications. Microphones designed
for Personal Computer (PC) use, sometimes called multimedia microphones, use a stereo
3.5 mm plug (though a mono source) with the ring receiving power via a resistor from
(normally) a 5 V supply in the computer; unfortunately, a number of incompatible
dynamic microphones are fitted with 3.5 mm plugs too. While few electret microphones
rival the best DC-polarized units in terms of noise level, this is not due to any inherent
limitation of the electret. Rather, mass production techniques needed to produce
microphones cheaply don't lend themselves to the precision needed to produce the
highest quality microphones, due to the tight tolerances required in internal dimensions.
These tolerances are the same for all condenser microphones, whether the DC, RF or
electret technology is used.
[edit] Dynamic microphone
Patti Smith singing into a Shure SM58 (dynamic cardioid type) microphone
Dynamic microphones work via electromagnetic induction. They are robust, relatively
inexpensive and resistant to moisture. This, coupled with their potentially high gain
before feedback makes them ideal for on-stage use.
Moving-coil microphones use the same dynamic principle as in a loudspeaker, only
reversed. A small movable induction coil, positioned in the magnetic field of a permanent
magnet, is attached to the diaphragm. When sound enters through the windscreen of the
microphone, the sound wave moves the diaphragm. When the diaphragm vibrates, the
coil moves in the magnetic field, producing a varying current in the coil through
electromagnetic induction. A single dynamic membrane will not respond linearly to all
audio frequencies. Some microphones for this reason utilize multiple membranes for the
different parts of the audio spectrum and then combine the resulting signals. Combining
the multiple signals correctly is difficult and designs that do this are rare and tend to be
expensive. There are on the other hand several designs that are more specifically aimed
towards isolated parts of the audio spectrum. The AKG D 112, for example, is designed
for bass response rather than treble.[3] In audio engineering several kinds of microphones
are often used at the same time to get the best result.
Edmund Lowe using a ribbon microphone
Ribbon microphones use a thin, usually corrugated metal ribbon suspended in a magnetic
field. The ribbon is electrically connected to the microphone's output, and its vibration
within the magnetic field generates the electrical signal. Ribbon microphones are similar
to moving coil microphones in the sense that both produce sound by means of magnetic
induction. Basic ribbon microphones detect sound in a bidirectional (also called figureeight) pattern because the ribbon, which is open to sound both front and back, responds to
the pressure gradient rather than the sound pressure. Though the symmetrical front and
rear pickup can be a nuisance in normal stereo recording, the high side rejection can be
used to advantage by positioning a ribbon microphone horizontally, for example above
cymbals, so that the rear lobe picks up only sound from the cymbals. Crossed figure 8, or
Blumlein pair, stereo recording is gaining in popularity, and the figure 8 response of a
ribbon microphone is ideal for that application.
Other directional patterns are produced by enclosing one side of the ribbon in an acoustic
trap or baffle, allowing sound to reach only one side. The classic RCA Type 77-DX
microphone has several externally-adjustable positions of the internal baffle, allowing the
selection of several response patterns ranging from "Figure-8" to "Unidirectional". Such
older ribbon microphones, some of which still give very high quality sound reproduction,
were once valued for this reason, but a good low-frequency response could only be
obtained if the ribbon was suspended very loosely, and this made them fragile. Modern
ribbon materials, including new nanomaterials[4] have now been introduced that eliminate
those concerns, and even improve the effective dynamic range of ribbon microphones at
low frequencies. Protective wind screens can reduce the danger of damaging a vintage
ribbon, and also reduce plosive artifacts in the recording. Properly designed wind screens
produce negligible treble attenuation. In common with other classes of dynamic
microphone, ribbon microphones don't require phantom power; in fact, this voltage can
damage some older ribbon microphones. Some new modern ribbon microphone designs
incorporate a preamplifier and, therefore, do require phantom power, and circuits of
modern passive ribbon microphones, i.e., those without the aforementioned preamplifier,
are specifically designed to resist damage to the ribbon and transformer by phantom
power. Also there are new ribbon materials available that are immune to wind blasts and
phantom power.
[edit] Carbon microphone
A carbon microphone is a capsule containing carbon granules pressed between two metal
plates. A voltage is applied across the metal plates, causing a small current to flow
through the carbon. One of the plates, the diaphragm, vibrates in sympathy with incident
sound waves, applying a varying pressure to the carbon. The changing pressure deforms
the granules, causing the contact area between each pair of adjacent granules to change,
and this causes the electrical resistance of the mass of granules to change. The changes in
resistance cause a corresponding change in the current flowing through the microphone,
producing the electrical signal. Carbon microphones were once commonly used in
telephones; they have extremely low-quality sound reproduction and a very limited
frequency response range, but are very robust devices.
Unlike other microphone types, the carbon microphone can also be used as a type of
amplifier, using a small amount of sound energy to produce a larger amount of electrical
energy. Carbon microphones found use as early telephone repeaters, making long
distance phone calls possible in the era before vacuum tubes. These repeaters worked by
mechanically coupling a magnetic telephone receiver to a carbon microphone: the faint
signal from the receiver was transferred to the microphone, with a resulting stronger
electrical signal to send down the line. (One illustration of this amplifier effect was the
oscillation caused by feedback, resulting in an audible squeal from the old "candlestick"
telephone if its earphone was placed near the carbon microphone.
[edit] Piezoelectric microphone
A crystal microphone uses the phenomenon of piezoelectricity — the ability of some
materials to produce a voltage when subjected to pressure — to convert vibrations into an
electrical signal. An example of this is Rochelle salt (potassium sodium tartrate), which is
a piezoelectric crystal that works as a transducer, both as a microphone and as a slimline
loudspeaker component. Crystal microphones were once commonly supplied with
vacuum tube (valve) equipment, such as domestic tape recorders. Their high output
impedance matched the high input impedance (typically about 10 megohms) of the
vacuum tube input stage well. They were difficult to match to early transistor equipment,
and were quickly supplanted by dynamic microphones for a time, and later small electret
condenser devices. The high impedance of the crystal microphone made it very
susceptible to handling noise, both from the microphone itself and from the connecting
cable.
Piezoelectric transducers are often used as contact microphones to amplify sound from
acoustic musical instruments, to sense drum hits, for triggering electronic samples, and to
record sound in challenging environments, such as underwater under high pressure.
Saddle-mounted pickups on acoustic guitars are generally piezoelectric devices that
contact the strings passing over the saddle. This type of microphone is different from
magnetic coil pickups commonly visible on typical electric guitars, which use magnetic
induction, rather than mechanical coupling, to pick up vibration.
[edit] Fiber optic microphone
The Optoacoustics 1140 fiber optic microphone
A fiber optic microphone converts acoustic waves into electrical signals by sensing
changes in light intensity, instead of sensing changes in capacitance or magnetic fields as
with conventional microphones.[5][6]
During operation, light from a laser source travels through an optical fiber to illuminate
the surface of a tiny, sound-sensitive reflective diaphragm. Sound causes the diaphragm
to vibrate, thereby minutely changing the intensity of the light it reflects. The modulated
light is then transmitted over a second optical fiber to a photo detector, which transforms
the intensity-modulated light into analog or digital audio for transmission or recording.
Fiber optic microphones possess high dynamic and frequency range, similar to the best
high fidelity conventional microphones.
Fiber optic microphones do not react to or influence any electrical, magnetic, electrostatic
or radioactive fields (this is called EMI/RFI immunity). The fiber optic microphone
design is therefore ideal for use in areas where conventional microphones are ineffective
or dangerous, such as inside industrial turbines or in magnetic resonance imaging (MRI)
equipment environments.
Fiber optic microphones are robust, resistant to environmental changes in heat and
moisture, and can be produced for any directionality or impedance matching. The
distance between the microphone's light source and its photo detector may be up to
several kilometers without need for any preamplifier and/or other electrical device,
making fiber optic microphones suitable for industrial and surveillance acoustic
monitoring.
Fiber optic microphones are used in very specific application areas such as for infrasound
monitoring and noise-canceling. They have proven especially useful in medical
applications, such as allowing radiologists, staff and patients within the powerful and
noisy magnetic field to converse normally, inside the MRI suites as well as in remote
control rooms.[7]) Other uses include industrial equipment monitoring and sensing, audio
calibration and measurement, high-fidelity recording and law enforcement.
[edit] Laser microphone
Laser microphones are often portrayed in movies as spy gadgets. A laser beam is aimed
at the surface of a window or other plane surface that is affected by sound. The slight
vibrations of this surface displace the returned beam, causing it to trace the sound wave.
The vibrating laser spot is then converted back to sound. In a more robust and expensive
implementation, the returned light is split and fed to an interferometer, which detects
frequency changes due to the Doppler effect. The former implementation is a tabletop
experiment; the latter requires an extremely stable laser and precise optics.
[edit] Liquid microphone
Main article: Water microphone
Early microphones did not produce intelligible speech, until Alexander Graham Bell
made improvements including a variable resistance microphone/transmitter. Bell's liquid
transmitter consisted of a metal cup filled with water with a small amount of sulfuric acid
added. A sound wave caused the diaphragm to move, forcing a needle to move up and
down in the water. The electrical resistance between the wire and the cup was then
inversely proportional to the size of the water meniscus around the submerged needle.
Elisha Gray filed a caveat for a version using a brass rod instead of the needle. Other
minor variations and improvements were made to the liquid microphone by Majoranna,
Chambers, Vanni, Sykes, and Elisha Gray, and one version was patented by Reginald
Fessenden in 1903. These were the first working microphones, but they were not
practical for commercial application. The famous first phone conversation between Bell
and Watson took place using a liquid microphone.
[edit] MEMS microphone
The MEMS (MicroElectrical-Mechanical System) microphone is also called a
microphone chip or silicon microphone. The pressure-sensitive diaphragm is etched
directly into a silicon chip by MEMS techniques, and is usually accompanied with
integrated preamplifier. Most MEMS microphones are variants of the condenser
microphone design. Often MEMS microphones have built in analog-to-digital converter
(ADC) circuits on the same CMOS chip making the chip a digital microphone and so
more readily integrated with modern digital products. Major manufacturers producing
MEMS silicon microphones are Wolfson Microelectronics (WM7xxx), Analog Devices,
Akustica (AKU200x), Infineon (SMM310 product), Knowles Electronics, Memstech
(MSMx), Sonion MEMS, and AAC Acoustic Technologies.[8]
[edit] Speakers as microphones
A loudspeaker, a transducer that turns an electrical signal into sound waves, is the
functional opposite of a microphone. Since a conventional speaker is constructed much
like a dynamic microphone (with a diaphragm, coil and magnet), speakers can actually
work "in reverse" as microphones. The result, though, is a microphone with poor quality,
limited frequency response (particularly at the high end), and poor sensitivity. In practical
use, speakers are sometimes used as microphones in applications where high quality and
sensitivity are not needed such as intercoms, walkie-talkies or XBOX Live chat
peripherals.
However, there is at least one other practical application of this principle: Using a
medium-size woofer placed closely in front of a "kick" (bass drum) in a drum set to act as
a microphone. The use of relatively large speakers to transduce low frequency sound
sources, especially in music production, is becoming fairly common. Since a relatively
massive membrane is unable to transduce high frequencies, placing a speaker in front of a
kick drum is often ideal for reducing cymbal and snare bleed into the kick drum sound.
Less commonly, microphones themselves can be used as speakers, almost always as
tweeters. This is less common, since microphones are not designed to handle the power
that speaker components are routinely required to cope with. One instance of such an
application was the STC microphone-derived 4001 super-tweeter, which was successfully
used in a number of high quality loudspeaker systems from the late 1960s to the mid-70s.
A well-known example of this use was the Bowers & Wilkins DM2a model.
[edit] Capsule design and directivity
The inner elements of a microphone are the primary source of differences in directivity.
A pressure microphone uses a diaphragm between a fixed internal volume of air and the
environment, and responds uniformly to pressure from all directions, so it is said to be
omnidirectional. A pressure-gradient microphone uses a diaphragm which is at least
partially open on both sides; the pressure difference between the two sides produces its
directional characteristics. Other elements such as the external shape of the microphone
and external devices such as interference tubes can also alter a microphone's directional
response. A pure pressure-gradient microphone is equally sensitive to sounds arriving
from front or back, but insensitive to sounds arriving from the side because sound
arriving at the front and back at the same time creates no gradient between the two. The
characteristic directional pattern of a pure pressure-gradient microphone is like a figure-8.
Other polar patterns are derived by creating a capsule that combines these two effects in
different ways. The cardioid, for instance, features a partially closed backside, so its
response is a combination of pressure and pressure-gradient characteristics.[9]
[edit] Microphone polar patterns
(Microphone facing top of page in diagram, parallel to page):
Omnidirectional
Subcardioid
CardioidSupercardioid
Hypercardioid Bi-directional or Figure of 8 Shotgun
A microphone's directionality or polar pattern indicates how sensitive it is to sounds
arriving at different angles about its central axis. The above polar patterns represent the
locus of points that produce the same signal level output in the microphone if a given
sound pressure level is generated from that point. How the physical body of the
microphone is oriented relative to the diagrams depends on the microphone design. For
large-membrane microphones such as in the Oktava (pictured above), the upward
direction in the polar diagram is usually perpendicular to the microphone body,
commonly known as "side fire" or "side address". For small diaphragm microphones such
as the Shure (also pictured above), it usually extends from the axis of the microphone
commonly known as "end fire" or "top/end address".
Some microphone designs combine several principles in creating the desired polar
pattern. This ranges from shielding (meaning diffraction/dissipation/absorption) by the
housing itself to electronically combining dual membranes.
[edit] Omnidirectional
An omnidirectional (or nondirectional) microphone's response is generally considered to
be a perfect sphere in three dimensions. In the real world, this is not the case. As with
directional microphones, the polar pattern for an "omnidirectional" microphone is a
function of frequency. The body of the microphone is not infinitely small and, as a
consequence, it tends to get in its own way with respect to sounds arriving from the rear,
causing a slight flattening of the polar response. This flattening increases as the diameter
of the microphone (assuming it's cylindrical) reaches the wavelength of the frequency in
question. Therefore, the smallest diameter microphone will give the best omnidirectional
characteristics at high frequencies.
The wavelength of sound at 10 kHz is little over an inch (3.4 cm) so the smallest
measuring microphones are often 1/4" (6 mm) in diameter, which practically eliminates
directionality even up to the highest frequencies. Omnidirectional microphones, unlike
cardioids, do not employ resonant cavities as delays, and so can be considered the
"purest" microphones in terms of low coloration; they add very little to the original
sound. Being pressure-sensitive they can also have a very flat low-frequency response
down to 20 Hz or below. Pressure-sensitive microphones also respond much less to wind
noise than directional (velocity sensitive) microphones.
An example of a nondirectional microphone is the round black eight ball.[10]
[edit] Unidirectional
An unidirectional microphone is sensitive to sounds from only one direction. The
diagram above illustrates a number of these patterns. The microphone faces upwards in
each diagram. The sound intensity for a particular frequency is plotted for angles radially
from 0 to 360°. (Professional diagrams show these scales and include multiple plots at
different frequencies. The diagrams given here provide only an overview of typical
pattern shapes, and their names.)
[edit] Cardioids
US664A University Sound Dynamic Supercardioid Microphone
The most common unidirectional microphone is a cardioid microphone, so named
because the sensitivity pattern is heart-shaped. A hyper-cardioid microphone is similar
but with a tighter area of front sensitivity and a smaller lobe of rear sensitivity. A supercardioid microphone is similar to a hyper-cardioid, except there is more front pickup and
less rear pickup. These three patterns are commonly used as vocal or speech
microphones, since they are good at rejecting sounds from other directions.
A cardioid microphone is effectively a superposition of an omnidirectional and a figure-8
microphone; for sound waves coming from the back, the negative signal from the figure8 cancels the positive signal from the omnidirectional element, whereas for sound waves
coming from the front, the two add to each other. A hypercardioid microphone is similar,
but with a slightly larger figure-8 contribution. Since pressure gradient transducer
microphones are directional, putting them very close to the sound source (at distances of
a few centimeters) results in a bass boost. This is known as the proximity effect[11]
[edit] Bi-directional
"Figure 8" or bi-directional microphones receive sound from both the front and back of
the element. Most ribbon microphones are of this pattern.
[edit] Shotgun
An Audio-Technica shotgun microphone
"Shotgun" microphones are the most highly directional. They have small lobes of
sensitivity to the left, right, and rear but are significantly less sensitive to the side and rear
than other directional microphones are. This results from placing the element at the end
of a tube with slots cut along the side; wave cancellation eliminates much of the off-axis
sound. Due to the narrowness of their sensitivity area, shotgun microphones are
commonly used on television and film sets, in stadiums, and for field recording of
wildlife.
[edit] Boundary or "PZM"
Several approaches have been developed for effectively using a microphone in less-thanideal acoustic spaces, which often suffer from excessive reflections from one or more of
the surfaces (boundaries) that make up the space. If the microphone is placed in, or in
very close proximity to, one of these boundaries, the reflections from that surface are not
sensed by the microphone. Initially this was done by placing an ordinary microphone
adjacent to the surface, sometimes in a block of acoustically transparent foam. Sound
engineers Ed Long and Ron Wickersham developed the concept of placing the diaphgram
parallel to and facing the boundary.[12] While the patent has expired, "Pressure Zone
Microphone" and "PZM" are still active trademarks of Crown International, and the
generic term "boundary microphone" is preferred. While a boundary microphone was
initially implemented using an omnidirectional element, it is also possible to mount a
directional microphone close enough to the surface to gain some of the benefits of this
technique while retaining the directional properties of the element. Crown's trademark on
this approach is "Phase Coherent Cardioid" or "PCC," but there are other makers who
employ this technique as well.
[edit] Application-specific designs
A lavalier microphone is made for hands-free operation. These small microphones are
worn on the body. Originally, they were held in place with a lanyard worn around the
neck, but more often they are fastened to clothing with a clip, pin, tape or magnet. The
lavalier cord may be hidden by clothes and either run to an RF transmitter in a pocket or
clipped to a belt (for mobile use), or run directly to the mixer (for stationary
applications).
A wireless microphone is one in which the artist is not limited by a cable. It usually sends
its signal using a small FM radio transmitter to a nearby receiver connected to the sound
system, but it can also use infrared light if the transmitter and receiver are within sight of
each other.
A contact microphone is designed to pick up vibrations directly from a solid surface or
object, as opposed to sound vibrations carried through air. One use for this is to detect
sounds of a very low level, such as those from small objects or insects. The microphone
commonly consists of a magnetic (moving coil) transducer, contact plate and contact pin.
The contact plate is placed against the object from which vibrations are to be picked up;
the contact pin transfers these vibrations to the coil of the transducer. Contact
microphones have been used to pick up the sound of a snail's heartbeat and the footsteps
of ants. A portable version of this microphone has recently been developed. A throat
microphone is a variant of the contact microphone, used to pick up speech directly from
the throat, around which it is strapped. This allows the device to be used in areas with
ambient sounds that would otherwise make the speaker inaudible.
A parabolic microphone uses a parabolic reflector to collect and focus sound waves onto
a microphone receiver, in much the same way that a parabolic antenna (e.g. satellite dish)
does with radio waves. Typical uses of this microphone, which has unusually focused
front sensitivity and can pick up sounds from many meters away, include nature
recording, outdoor sporting events, eavesdropping, law enforcement, and even espionage.
Parabolic microphones are not typically used for standard recording applications, because
they tend to have poor low-frequency response as a side effect of their design.
A stereo microphone integrates two microphones in one unit to produce a stereophonic
signal. A stereo microphone is often used for broadcast applications or field recording
where it would be impractical to configure two separate condenser microphones in a
classic X-Y configuration (see microphone practice) for stereophonic recording. Some
such microphones have an adjustable angle of coverage between the two channels.
A noise-canceling microphone is a highly directional design intended for noisy
environments. One such use is in aircraft cockpits where they are normally installed as
boom microphones on headsets. Another use is on loud concert stages for vocalists.
Many noise-canceling microphones combine signals received from two diaphragms that
are in opposite electrical polarity or are processed electronically. In dual diaphragm
designs, the main diaphragm is mounted closest to the intended source and the second is
positioned farther away from the source so that it can pick up environmental sounds to be
subtracted from the main diaphragm's signal. After the two signals have been combined,
sounds other than the intended source are greatly reduced, substantially increasing
intelligibility. Other noise-canceling designs use one diaphragm that is affected by ports
open to the sides and rear of the microphone, with the sum being a 16 dB rejection of
sounds that are farther away. One noise-canceling headset design using a single
diaphragm has been used prominently by vocal artists such as Garth Brooks and Janet
Jackson.[13] A few noise-canceling microphones are throat microphones.
[edit] Connectors
Electronic symbol for a microphone.
The most common connectors used by microphones are:
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Male XLR connector on professional microphones
¼ inch (sometimes referred to as 6.5 mm) jack plug also known as 1/4 inch TRS
connector on less expensive consumer microphones. Many consumer
microphones use an unbalanced 1/4 inch phone jack. Harmonica microphones
commonly use a high impedance 1/4 inch TS connection to be run through guitar
amplifiers.
3.5 mm (sometimes referred to as 1/8 inch mini) stereo (wired as mono) mini
phone plug on very inexpensive and computer microphones
Some microphones use other connectors, such as a 5-pin XLR, or mini XLR for
connection to portable equipment. Some lavalier (or 'lapel', from the days of attaching the
microphone to the news reporters suit lapel) microphones use a proprietary connector for
connection to a wireless transmitter. Since 2005, professional-quality microphones with
USB connections have begun to appear, designed for direct recording into computerbased software.
[edit] Impedance-matching
Microphones have an electrical characteristic called impedance, measured in ohms (Ω),
that depends on the design. Typically, the rated impedance is stated.[14] Low impedance
is considered under 600 Ω. Medium impedance is considered between 600 Ω and 10 kΩ.
High impedance is above 10 kΩ. Condenser microphones typically have an output
impedance between 50 and 200 ohms.[15]
The output of a given microphone delivers the same power whether it is low or high
impedance. If a microphone is made in high and low impedance versions, the high
impedance version will have a higher output voltage for a given sound pressure input,
and is suitable for use with vacuum-tube guitar amplifiers, for instance, which have a
high input impedance and require a relatively high signal input voltage to overcome the
tubes' inherent noise. Most professional microphones are low impedance, about 200 Ω or
lower. Professional vacuum-tube sound equipment incorporates a transformer that steps
up the impedance of the microphone circuit to the high impedance and voltage needed to
drive the input tube; the impedance conversion inherently creates voltage gain as well.
External matching transformers are also available that can be used in-line between a low
impedance microphone and a high impedance input.
Low-impedance microphones are preferred over high impedance for two reasons: one is
that using a high-impedance microphone with a long cable will result in loss of high
frequency signal due to the capacitance of the cable which forms a low-pass filter with
the microphone output impedance; the other is that long high-impedance cables tend to
pick up more hum (and possibly radio-frequency interference (RFI) as well). Nothing
will be damaged if the impedance between microphone and other equipment is
mismatched; the worst that will happen is a reduction in signal or change in frequency
response.
Most microphones are designed not to have their impedance matched by the load to
which they are connected;[16] doing so can alter their frequency response and cause
distortion, especially at high sound pressure levels. Certain ribbon and dynamic
microphones are exceptions, due to the designers' assumption of a certain load impedance
being part of the internal electro-acoustical damping circuit of the microphone.[17]
[edit] Digital microphone interface
The AES 42 standard, published by the Audio Engineering Society, defines a digital
interface for microphones. Microphones conforming to this standard directly output a
digital audio stream through an XLR male connector, rather than producing an analog
output. Digital microphones may be used either with new equipment which has the
appropriate input connections conforming to the AES 42 standard, or else by use of a
suitable interface box. Studio-quality microphones which operate in accordance with the
AES 42 standard are now appearing from a number of microphone manufacturers.
[edit] Measurements and specifications
A comparison of the far field on-axis frequency response of the Oktava 319 and the
Shure SM58
Because of differences in their construction, microphones have their own characteristic
responses to sound. This difference in response produces non-uniform phase and
frequency responses. In addition, microphones are not uniformly sensitive to sound
pressure, and can accept differing levels without distorting. Although for scientific
applications microphones with a more uniform response are desirable, this is often not the
case for music recording, as the non-uniform response of a microphone can produce a
desirable coloration of the sound. There is an international standard for microphone
specifications,[14] but few manufacturers adhere to it. As a result, comparison of
published data from different manufacturers is difficult because different measurement
techniques are used. The Microphone Data Website has collated the technical
specifications complete with pictures, response curves and technical data from the
microphone manufacturers for every currently listed microphone, and even a few
obsolete models, and shows the data for them all in one common format for ease of
comparison.[1]. Caution should be used in drawing any solid conclusions from this or
any other published data, however, unless it is known that the manufacturer has supplied
specifications in accordance with IEC 60268-4.
A frequency response diagram plots the microphone sensitivity in decibels over a range
of frequencies (typically at least 0–20 kHz), generally for perfectly on-axis sound (sound
arriving at 0° to the capsule). Frequency response may be less informatively stated
textually like so: "30 Hz–16 kHz ±3 dB". This is interpreted as a (mostly) linear plot
between the stated frequencies, with variations in amplitude of no more than plus or
minus 3 dB. However, one cannot determine from this information how smooth the
variations are, nor in what parts of the spectrum they occur. Note that commonly-made
statements such as "20 Hz–20 kHz" are meaningless without a decibel measure of
tolerance. Directional microphones' frequency response varies greatly with distance from
the sound source, and with the geometry of the sound source. IEC 60268-4 specifies that
frequency response should be measured in plane progressive wave conditions (very far
away from the source) but this is seldom practical. Close talking microphones may be
measured with different sound sources and distances, but there is no standard and
therefore no way to compare data from different models unless the measurement
technique is described.
The self-noise or equivalent noise level is the sound level that creates the same output
voltage as the microphone does in the absence of sound. This represents the lowest point
of the microphone's dynamic range, and is particularly important should you wish to
record sounds that are quiet. The measure is often stated in dB(A), which is the
equivalent loudness of the noise on a decibel scale frequency-weighted for how the ear
hears, for example: "15 dBA SPL" (SPL means sound pressure level relative to
20 micropascals). The lower the number the better. Some microphone manufacturers
state the noise level using ITU-R 468 noise weighting, which more accurately represents
the way we hear noise, but gives a figure some 11–14 dB higher. A quiet microphone will
measure typically 20 dBA SPL or 32 dB SPL 468-weighted. Very quiet microphones
have existed for years for special applications, such the Brüel & Kjaer 4179, with a noise
level around 0 dB SPL. Recently some microphones with low noise specifications have
been introduced in the studio/entertainment market, such as models from Neumann and
Røde that advertise noise levels between 5–7 dBA. Typically this is achieved by altering
the frequency response of the capsule and electronics to result in lower noise within the
A-weighting curve while broadband noise may be increased.
The maximum SPL (sound pressure level) the microphone can accept is measured for
particular values of total harmonic distortion (THD), typically 0.5%. This is generally
inaudible, so one can safely use the microphone at this level without harming the
recording. Example: "142 dB SPL peak (at 0.5% THD)". The higher the value, the better,
although microphones with a very high maximum SPL also have a higher self-noise.
The clipping level is perhaps a better indicator of maximum usable level,[citation needed] as
the 1% THD figure usually quoted under max SPL is really a very mild level of
distortion, quite inaudible especially on brief high peaks. Harmonic distortion from
microphones is usually of low-order (mostly third harmonic) type, and hence not very
audible even at 3-5%. Clipping, on the other hand, usually caused by the diaphragm
reaching its absolute displacement limit (or by the preamplifier), will produce a very
harsh sound on peaks, and should be avoided if at all possible. For some microphones the
clipping level may be much higher than the max SPL.
The dynamic range of a microphone is the difference in SPL between the noise floor and
the maximum SPL. If stated on its own, for example "120 dB", it conveys significantly
less information than having the self-noise and maximum SPL figures individually.
Sensitivity indicates how well the microphone converts acoustic pressure to output
voltage. A high sensitivity microphone creates more voltage and so will need less
amplification at the mixer or recording device. This is a practical concern but is not
directly an indication of the mic's quality, and in fact the term sensitivity is something of
a misnomer, 'transduction gain' being perhaps more meaningful, (or just "output level")
because true sensitivity will generally be set by the noise floor, and too much
"sensitivity" in terms of output level will compromise the clipping level. There are two
common measures. The (preferred) international standard is made in millivolts per pascal
at 1 kHz. A higher value indicates greater sensitivity. The older American method is
referred to a 1 V/Pa standard and measured in plain decibels, resulting in a negative
value. Again, a higher value indicates greater sensitivity, so −60 dB is more sensitive
than −70 dB.
[edit] Measurement microphones
Some microphones are intended for testing speakers, measuring noise levels and
otherwise quantifying an acoustic experience. These are calibrated transducers and will
usually be supplied with a calibration certificate stating absolute sensitivity against
frequency. The quality of measurement microphones is often referred to using the
designations "Class 1," "Type 2" etc., which are references not to microphone
specifications but to sound level meters.[18] A more comprehensive standard[19] for the
description of measurement microphone performance was recently adopted.
Measurement microphones are generally scalar sensors of pressure; they exhibit an
omnidirectional response, limited only by the scattering profile of their physical
dimensions. Sound intensity or sound power measurements require pressure-gradient
measurements, which are typically made using arrays of at least two microphones, or
with hot-wire anemometers.
[edit] Microphone calibration techniques
Like most manufactured products there can be variations, which may change over the
lifetime of the device. Accordingly, it is regularly necessary to test the test microphones.
This service is offered by some microphone manufacturers and by independent certified
testing labs. Microphone calibration is ultimately traceable to primary standards at one of
the national laboratories such as PTB in Germany and NIST in the USA. Some test
enough microphones to justify an in-house calibration lab. Depending on the application,
measurement microphones must be tested periodically (every year or several months,
typically) and after any potentially damaging event, such as being dropped (most such
mikes come in foam-padded cases to reduce this risk) or exposed to sounds beyond the
acceptable level.
[edit] Pistonphone apparatus
A pistonphone is an acoustical calibrator (sound source) using a closed coupler to
generate a precise sound pressure for the calibration of instrumentation microphones. The
principle relies on a piston mechanically driven to move at a specified cyclic rate, on a
fixed volume of air to which the microphone under test is exposed. The air is assumed to
be compressed adiabatically and the sound pressure level in the chamber can be
calculated from internal physical dimensions of the device and the adiabatic gas law,
which requires that the product of the pressure P with V raised to the power gamma be
constant; here gamma is the ratio of the specific heat of air at constant pressure to its
specific heat at constant volume. The pistonphone method only works at low frequencies,
but it can be accurate and yields an easily calculable sound pressure level. The standard
test frequency is usually around 250 Hz.
[edit] Reciprocal method
This method relies on the reciprocity of one or more microphones in a group of 3 to be
calibrated. It can be performed in a closed coupler or in the free field. Only one of the
microphones need be reciprocal (exhibits equal response when used as a microphone or
as a loudspeaker).
[edit] Microphone array and array microphones
Main article: Microphone array
A microphone array is any number of microphones operating in tandem. There are many
applications:
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Systems for extracting voice input from ambient noise (notably telephones,
speech recognition systems, hearing aids)
Surround sound and related technologies
Locating objects by sound: acoustic source localization, e.g. military use to locate
the source(s) of artillery fire. Aircraft location and tracking.
High fidelity original recordings
3D spatial beamforming for localized acoustic detection of subcutaneous sounds
Typically, an array is made up of omnidirectional microphones distributed about the
perimeter of a space, linked to a computer that records and interprets the results into a
coherent form.
[edit] Microphone windscreens
Windscreens are used to protect microphones that would otherwise be buffeted by wind
or vocal plosives from consonants such as "P", "B", etc. Most microphones have an
integral windscreen built around the microphone diaphragm. A screen of plastic, wire
mesh or a metal cage is held at a distance from the microphone diaphragm, to shield it.
This cage provides a first line of defense against the mechanical impact of objects or
wind. Some microphones, such as the Shure SM58, may have an additional layer of foam
inside the cage to further enhance the protective properties of the shield. Beyond integral
microphone windscreens, there are three broad classes of additional wind protection.
One disadvantage of all windscreen types is that the microphone's high frequency
response is attenuated by a small amount, depending on the density of the protective
layer.
[edit] Microphone covers
Microphone covers are often made of soft open-cell polyester or polyurethane foam
because of the inexpensive, disposable nature of the foam. Optional windscreens are
often available from the manufacturer and third parties. A very visible example of an
optional accessory windscreen is the A2WS from Shure, one of which is fitted over each
of the two Shure SM57 microphones used on the United States president's lectern.[20] One
disadvantage of polyurethane foam microphone covers is that they can deteriorate over
time. Windscreens also tend to collect dirt and moisture in their open cells and must be
cleaned to prevent high frequency loss, bad odor and unhealthy conditions for the person
using the microphone. On the other hand, a major advantage of concert vocalist
windscreens is that one can quickly change to a clean windscreen between users,
reducing the chance of transferring germs. Windscreens of various colors can be used to
distinguish one microphone from another on a busy, active stage.
[edit] Pop filters
Pop filters or pop screens are used in controlled studio environments to minimize
plosives when recording. A typical pop filter is composed of one or more layers of
acoustically transparent gauze-like material, such as woven nylon stretched over a
circular frame and a clamp and a flexible mounting bracket to attach to the microphone
stand. The pop shield is placed between the vocalist and the microphone. The need for a
pop filter increases the closer a vocalist brings his lips the microphone. Singers can be
trained either to soften their plosives or direct the air blast away from the microphone, in
which cases they don't need a pop filter.
Pop filters also keep spittle off the microphone. Most condenser microphones can be
damaged by spittle.
[edit] Blimps
Blimps (also known as Zeppelins) are large, hollow windscreens used to surround
microphones for outdoor location audio, such as nature recording, electronic news
gathering, and for film and video shoots. They can cut wind noise by as much as 25 dB,
especially low-frequency noise. The blimp is essentially a hollow cage or basket with
acoustically transparent material stretched over the outer frame. The blimp works by
creating a volume of still air around the microphone. The microphone is often further
isolated from the blimp by an elastic suspension inside the basket. This reduces wind
vibrations and handling noise transmitted from the cage. To extend the range of wind
speed conditions in which the blimp will remain effective, many have the option of fitting
a secondary cover over the outer shell. This is usually an acoustically transparent,
synthetic fur material with long, soft hairs. The hairs act as shock absorbers to any wind
turbulence hitting the blimp. A synthetic fur cover can reduce wind noise by an additional
12 dB.[21]
[edit] See also
Electronics portal
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Loudspeaker (the inverse of a microphone)
Hydrophone (microphone for underwater use)
Geophone (microphone for use within the earth)
Ionophone (plasma-based microphone)
Microphone connector
Microphone practice
Microphone preamplifier
A-weighting
Button microphone
ITU-R 468 noise weighting
Nominal impedance — Information about impedance matching for audio
components
Sound pressure level
Wireless microphone
XLR connector — The 3-pin variant of which is used for connecting microphones
Shock mount - A microphone mount in which the microphone is suspended by
elastic
5 : Camera
From Wikipedia, the free encyclopedia
Jump to: navigation, search
For other uses, see Camera (disambiguation).
Cameras from Large to Small, Film to Digital
A camera is a device that records images, either as a still photograph or as moving
images known as videos or movies. The term comes from the camera obscura (Latin for
"dark chamber"), an early mechanism of projecting images where an entire room
functioned as a real-time imaging system; the modern camera evolved from the camera
obscura.
Cameras may work with the light of the visible spectrum or with other portions of the
electromagnetic spectrum. A camera generally consists of an enclosed hollow with an
opening (aperture) at one end for light to enter, and a recording or viewing surface for
capturing the light at the other end. A majority of cameras have a lens positioned in front
of the camera's opening to gather the incoming light and focus all or part of the image on
the recording surface. The diameter of the aperture is often controlled by a diaphragm
mechanism, but some cameras have a fixed-size aperture.
A typical still camera takes one photo each time the user presses the shutter button. A
typical movie camera continuously takes 24 film frames per second as long as the user
holds down the shutter button.
[edit] History
Main article: History of the camera
Camera obscura.
The forerunner to the camera was the camera obscura.[1] The camera obscura is an
instrument consisting of a darkened chamber or box, into which light is admitted through
a convex lens, forming an image of external objects on a surface of paper or glass, etc.,
placed at the focus of the lens.[2] The camera obscura was described by the Arabic
scientist Ibn al-Haytham (Alhazen) in his Book of Optics (1015–1021).[3] Alhazen's work
appeared in Latin translation as De Aspectibus ("Concerning vision") in about 1200, and
the book influenced Roger Bacon's reflections on producing images using pinholes.
Bacon's notes and drawings, published as Perspectiva in 1267, are partly clouded with
theological material describing how the Devil can insinuate himself through the smallest
of spaces by magic,[4] and it is not clear whether or not he produced such a device. On 24
January 1544 mathematician and instrument maker Reiners Gemma Frisius of Leuven
University used one to watch a solar eclipse, publishing a diagram of his method in De
Radio Astronimica et Geometrico in the following year.[5] In 1558 Giovanni Batista della
Porta was the first to recommend the method as an aid to drawing.[6] The actual name of
camera obscura was first applied to the technique by mathematician and astronomer
Johannes Kepler in his Ad Vitellionem paralipomena of 1604; he would later improve the
apparatus by adding a lens and making it transportable, in the form of a tent.[7][8] Irish
scientist Robert Boyle and his assistant Robert Hooke later developed a portable camera
obscura in the 1660s.[9]
The first camera that was small and portable enough to be practical for photography was
built by Johann Zahn in 1685, though it would be almost 150 years before technology
caught up to the point where this was practical. Early photographic cameras were
essentially similar to Zahn's model, though usually with the addition of sliding boxes for
focusing. Before each exposure, a sensitized plate would be inserted in front of the
viewing screen to record the image. Jacques Daguerre's popular daguerreotype process
utilized copper plates, while the calotype process invented by William Fox Talbot
recorded images on paper.
The first permanent colour photograph, taken by James Clerk Maxwell in 1861.
The first permanent photograph was made in 1826 by Joseph Nicéphore Niépce using a
sliding wooden box camera made by Charles and Vincent Chevalier in Paris. Niépce built
on a discovery by Johann Heinrich Schultz (1724): a silver and chalk mixture darkens
under exposure to light. However, while this was the birth of photography, the camera
itself can be traced back much further. Before the invention of photography,there was no
way to preserve the images produced by these cameras apart from manually tracing them.
The development of the collodion wet plate process by Frederick Scott Archer in 1850
cut exposure times dramatically, but required photographers to prepare and develop their
glass plates on the spot, usually in a mobile darkroom. Despite their complexity, the wetplate ambrotype and tintype processes were in widespread use in the latter half of the
19th century. Wet plate cameras were little different from previous designs, though there
were some models, such as the sophisticated Dubroni of 1864, where the sensitizing and
developing of the plates could be carried out inside the camera itself rather than in a
separate darkroom. Other cameras were fitted with multiple lenses for making cartes de
visite. It was during the wet plate era that the use of bellows for focusing became
widespread.
The first colour photograph was made by Scottish physicist James Clerk Maxwell, with
the help of English inventor and photographer Thomas Sutton, in 1861[10]
[edit] Mechanics
[edit] Image capture
see also Photographic lens design
19th century studio camera, with bellows for focusing.
Traditional cameras capture light onto photographic film or photographic plate. Video
and digital cameras use electronics, usually a charge coupled device (CCD) or sometimes
a CMOS sensor to capture images which can be transferred or stored in tape or computer
memory inside the camera for later playback or processing.
Cameras that capture many images in sequence are known as movie cameras or as ciné
cameras in Europe; those designed for single images are still cameras. However these
categories overlap. As still cameras are often used to capture moving images in special
effects work and modern digital cameras are often able to trivially switch between still
and motion recording modes. A video camera is a category of movie camera that captures
images electronically (either using analogue or digital technology).
[edit] Lens
Main article: Photographic lens
Main article: Photographic lens design
The lens of a camera captures the light from the subject and brings it to a focus on the
film or detector. The design and manufacture of the lens is critical to the quality of the
photograph being taken. The technological revolution in camera design in the 18th
century revolutionized optical glass manufacture and lens design with great benefits for
modern lens manufacture in a wide range of optical instruments from reading glasses to
microscopes. Pioneers included Zeiss and Leitz.
[edit] Focus
Auto-focus systems can capture a subject a variety of ways; here, the focus is on the
person's image in the mirror.
Due to the optical properties of photographic lenses, only objects within a limited range
of distances from the camera will be reproduced clearly. The process of adjusting this
range is known as changing the camera's focus. There are various ways of focusing a
camera accurately. The simplest cameras have fixed focus and use a small aperture and
wide-angle lens to ensure that everything within a certain range of distance from the lens,
usually around 3 metres (10 ft) to infinity, is in reasonable focus. Fixed focus cameras are
usually inexpensive types, such as single-use cameras. The camera can also have a
limited focusing range or scale-focus that is indicated on the camera body. The user will
guess or calculate the distance to the subject and adjust the focus accordingly. On some
cameras this is indicated by symbols (head-and-shoulders; two people standing upright;
one tree; mountains).
Rangefinder cameras allow the distance to objects to be measured by means of a coupled
parallax unit on top of the camera, allowing the focus to be set with accuracy. Single-lens
reflex cameras allow the photographer to determine the focus and composition visually
using the objective lens and a moving mirror to project the image onto a ground glass or
plastic micro-prism screen. Twin-lens reflex cameras use an objective lens and a focusing
lens unit (usually identical to the objective lens.) in a parallel body for composition and
focusing. View cameras use a ground glass screen which is removed and replaced by
either a photographic plate or a reusable holder containing sheet film before exposure.
Modern cameras often offer autofocus systems to focus the camera automatically by a
variety of methods e.g. by fishing.[11]
[edit] Exposure control
The size of the aperture and the brightness of the scene controls the amount of light that
enters the camera during a period of time, and the shutter controls the length of time that
the light hits the recording surface. Equivalent exposures can be made with a larger
aperture and a faster shutter speed or a corresponding smaller aperture and with the
shutter speed slowed down.
[edit] Shutters
Main article: Shutter (photography)
Although a range of different shutter devices have been used during the development of
the camera only two types have been widely used and remain in use today.
The focal plane shutter operates as close to the film plane as possible and consists of
cloth curtains that are pulled across the film plane with a carefully determined gap
between the two curtains or consisting of a series of metal plates moving either vertically
or horizontally across the film plan. As the curtains or blades move at a constant speed,
exposing the whole film plane can takes much longer than the exposure time. For
example an exposure of 1/1000 second may be achieved by the shutter curtains moving
across the film plane in 1/50th of a second but with the two curtains only separated by
1/20th of the frame width. When photographing rapidly moving objects, the use of a focal
plane shutter can produce some unexpected effects. Focal plane shutters are also difficult
to synchronise with electronic flash and it is often only possible to use flash at shutter
speeds below 1/60th second although in some modern cameras that can be as fast as
1/100second/
The Copal shutter or more precisely the in-lens shutter is a shutter contained within the
lens structure, often close to the diaphragm consisting of a number of metal leaves which
are maintained under spring tension and which are opened and then closed when the
shutter is released. The exposure time is determined by the interval between opening and
closing. In this shutter design, the whole film frame is exposed at one time. This makes
flash synchronisation much simpler as the flash only needs to fire once the shutter is fully
open. This disadvantage of such shutters is their inability to reliably produce very fast
shutter speeds and the additional cost and weight of having to include a shutter
mechanism for every lens.
[edit] Film formats
Main article: Film formats
A wide range of film and plate formats have been used by cameras. In the early history
plate sizes were often specific for the make and model of camera although there quickly
developed some standardisation for the more popular cameras. The introduction of rollfilm drove the standardisation process still further so that by the 1950s only a few
standard roll films were in use. These included 120 film providing 8, 12 or 16 exposures,
220 film providing 16 or 24 exposures, 127 film providing 8 exposures , principally in
Brownie 125 cameras and 35mm film providing 12, 20 or 36 exposures - or up to 72
exposures in bulk cassettes for the Leica range.
For cine cameras, 35mm film was the original film format but 16mm film soon followed
produced by cutting 35mm in two. An early amateur format was 9.5mm. Later formats
included 8mm film and Super 8.
[edit] Camera designs
[edit] Plate camera
The earliest cameras produced in significant numbers used sensitised glass plates and are
now termed plate cameras. Light entered a lens mounted on a lens board which was
separated from the plate by an extendible bellows. Many of these cameras, had controls
to raise or lower the lens and to tilt it forwards or backwards to control perspective .
Focussing of these plate cameras was by the use of a ground glass screen at the point of
focus. Because lens design only allowed rather small aperture lenses, the image on the
ground glass screen was faint and most photographers had a dark cloth to cover their
heads to allow focussing and composition to be carried out more easily. When focus and
composition were satisfactory, the ground glass screen was removed and a sensitised
plate put in its place protected by a dark slide (photography) . To make the exposure, the
dark slide was carefully slid out and the shutter opened and then closed and the dark-slide
replaced. In current designs the plate camera is best represented by the view camera.
[edit] Large format camera
Main article: View camera
The large format camera is a direct successor of the early plate cameras and remain in use
for high quality photography and for technical, architectural and industrial photography.
There are three common types, the monorail camera, the field camera and the press
camera. All use large format sheets of film, although there are backs for medium format
120-film available for most systems, and have an extensible bellows with the lens and
shutter mounted on a lens plate at the front. These cameras have a wide range of
movements allowing very close control of focus and perspective.
[edit] Medium format camera
Main article: Medium-format
The medium-format cameras has a film negative size somewhere in between the large
format cameras and the smaller 35mm cameras. Typically these systems use 120- or 220film. The most common sizes being 6x4.5 cm, 6x6 cm and 6x7 cm. The designs of this
kind of camera shows greater variation than their larger brethren. Ranging from monorail
systems, via the classic Hasselblad model with separate backs, to smaller rangefinder
cameras. There are even compact amateur cameras available in this format.
[edit] Folding camera
The introduction of films enabled the existing designs for plate cameras to be made much
smaller and for the base-plate to be hinged so that it could be folded up compressing the
bellows. These designs were very compact and small models were dubbed Vest pocket
cameras.
[edit] Box camera
Box cameras were introduced as a budget level camera and had few if any controls. The
original box Brownie models had a small reflex viewfinder mounted on the top of the
camera and had no aperture or focussing controls and just a simple shutter. Later models
such as the Brownie 127 had larger direct view optical viewfinders together with a curved
film path to help
[edit] Rangefinder camera
Main article: Rangefinder camera
As camera and lens technology developed and wide aperture lenses became more
common range-finder cameras were introduced to make focussing more precise. The
range finder had two separated viewfinder windows one of which was linked to the
focusing mechanisms and moved right or left as the focussing ring was turned. The two
separate images were brought together on a ground glass viewing screen. When vertical
lines in the object being photographed met exactly in the combined image, the object was
in focus. A normal composition viewfinder was also provided.
[edit] Single-lens reflex
Main article: Single-lens reflex camera
In the single-lens reflex camera the photographer see the scene through the camera lens.
This avoids the problems of parallax which occurs when the viewfinder or viewing lens is
separated from the taking lens. Single-lens reflex cameras have been made in several
formats including 220/120 taking 8, 12 or 16 photographs on a 120 roll and twice that
number of a 220 film. These correspond to 6x9, 6x6 and 6x4.5 respectively (all
dimensions in cm). Notable manufacturers of large format SLR include Hasselblad,
Mamiya, Bronica and Pentax. However the most common format of SLRs has been
35 mm and subsequently the migration to digital SLRs, using almost identical sized
bodies and sometimes using the same lens systems.
Almost all SLR used a front surfaced mirror in the optical path to direct the light from the
lens via a viewing screen and pentaprism to the eyepiece. At the time of exposure the
mirror flipped up out of the light path before the shutter opened. Some early cameras
experimented other methods of providing through the lens viewing including the use of a
semi transparent pellicle as in the Canon Pellix [12] and others with a small periscope such
as in the Corfield Periflex series[13]
[edit] Twin-lens reflex
Main article: Twin-lens reflex camera
Twin-lens reflex cameras used a pair of nearly identical lenses, one to form the image and
one as a viewfinder. The lens were arranged with the viewing lens immediately above the
taking lens. The viewing lens projects an image onto a viewing screen which can be seen
from above. Some manufacturers such as Mamiya also provided a reflex head to attach to
the viewing screen to all the camera to be held to the eye when in use. The advantage of a
TLR was that it could be easily focussed using the viewing screen and that under most
circumstances the view seen in the viewing screen was identical to that recorded on film.
At close distances however, parallax errors were encountered and some cameras also
included an indicator to show what part of the composition would be excluded.
Some TLR had interchangeable lenses but as these had to be paired lenses they were
relatively heavy and did not provide the range of focal lengths that the SLR could
support. Although most TLRs used 120 or 220 film some used 127 film.
[edit] Ciné camera
Main article: Movie camera
A ciné camera or movie camera is a type of photographic camera which takes a rapid
sequence of photographs on strips of film. In contrast to a still camera, which captures a
single snapshot at a time, the ciné camera takes a series of images, each called a "frame"
through the use of an intermittent mechanism. The frames are later played back in a ciné
projector at a specific speed, called the "frame rate" (number of frames per second).
While viewing, a person's eyes and brain merge the separate pictures together to create
the illusion of motion. The first ciné camera was built around 1888 and by 1890 several
types were being manufactured. The standard film size for ciné cameras was quickly
established as 35mm film and this remains in use to this day. Other professional standard
formats include 70 mm film and 16mm film whilst amateurs film makers have used 9.5
mm film, 8mm film or Standard 8 and Super 8 before the move into digital format. The
size and complexity of ciné cameras varies greatly depending on the uses required of the
camera. Some professional equipment is very large and too heavy to be hand held whilst
some amateur cameras were designed to be as small and light as possible enabling singlehanded operation.
[edit] Image gallery
1921 Kodak
Opened up Cine
Kodak, used 35mm Silvestri Flexicam
movie film
Contax S of 1949 — 1952 Voigtlander
the world's first
Vito II
pentaprism SLR
Asahiflex IIa of
1955
Voigtländer Brillant
twin-lens reflex camera.
Kodak Retina IIIC of
1957
1988 A Soviet-era
Nikon F of 1959 —
the first 35mm
Voigtländer Vitoret LOMO LC-A
camera
system camera
of 1962
2003 — Canon EOS
300D, a model that
sparked the popularity of
consumer-level DSLRs
[edit] See also
[edit] Types
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Digital camera
Game camera
IP camera
Movie camera
Pinhole camera
Pocket camera
Rangefinder camera
Single-lens reflex camera
Toy camera
Trail camera
Twin-lens reflex camera
Video camera
View camera
Camera phone
[edit] Brands
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Adox[citation
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needed]
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AgfaPhoto
Agilux[citation
needed]
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Aigo
Aiptek
Alpa
Altisa[citation
needed]
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ArcaSwiss[citation
needed]
Clairex[citation
needed]
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Contax
Corfield
Coronet Camera
Company
Diana camera
Ducati Sogno
Eastman Kodak
Ebony cameras
Edixa
Ensign
Cameras[citation
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Holga
Honeywell
Horseman
USA[citation
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Ilford Photo
Imaging
Solutions
Group[citation
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needed]
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Kodak
Konica
Minolta
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needed]
needed]
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Nikon
Norcent[citation
Olympus
Corporation
Oregon
Scientific
Osaka
(camera)[citation
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needed]
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Panasonic
Pentax
Petri Camera
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Sharp
Sigma
Corpo
Silves
camer
Sinar
Sony
Tessin
Thorn
Pickar
Topco
Travel
(came
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Argus (camera
company)
Asahiflex
Balda KameraWerk[citation
needed]
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BenQ
Bolex
Bronica
Burke &
James[citation
needed]
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Exakta
FED (camera)
Fujica
Fujifilm
Gami
Gateway, Inc.
Graflex
Hasselblad
HewlettPackard
needed]
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Cambo
Photographic
Industry[citation
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Canon
(company)
Carl Braun
camera-werk
Casio
[edit] Other
Photography portal
Film portal
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Flash (photography)
Photographic filter
Tripod (photography)
Viewfinder
cameras in mobile phones
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Leica Camera
Leidolf
Linhof
LOMO
Lumix
Mamiya
Micro
Precision
Products
Minolta
Minox
Miranda
Camera
Company
Mustek
Systems
Newman &
Guardia
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Plaubel Makina
Polaroid
Corporation
Praktica
Promaster
(camera)[citation
needed]
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Ricoh
Rollei
Samsung Group
SatuGo[citation
needed]
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Seagull Camera
Van
Oosbr
needed]
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Reid and Sigrist
Regula[citation
needed]
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needed]
Vivita
Voigtl
Wisne
Comp
needed]
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Wray
Yashic
Zeiss
Zenit (
Zorki