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Camera

Camera

:This is the article about the photographing device. For other uses, see CAMERA. rightA camera is a device used to take pictures (usually photographs), either singly or in sequence, with or without sound recording, such as with video cameras. A camera that takes pictures singly is sometimes called a photo camera to distinguish it from a video camera. The name is derived from camera obscura, Latin for "dark chamber", an early mechanism for projecting images in which an entire room functioned much as the internal workings of a modern photographic camera, except there was no way at this time to record the image short of manually tracing it. Cameras may work with the visual spectrum or other portions of the electromagnetic spectrum.

Description

Every camera consists of some kind of enclosed chamber, with an opening or aperture at one end for light to enter, and a recording or viewing surface for capturing the light at the other end. This diameter of the aperture is often controlled by an diaphragm mechanism, but some cameras have a fixed-size aperture. While the size of the aperture and the brightness of the scene control the amount of light that enters the camera during photographing, the shutter controls the length of time that the light hits the recording surface. For example, in lower light situations, the shutter speed should be slower (longer time spent open) to allow the film to capture what little light is present. 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 feet) to infinity) is in reasonable focus. This is usually the kind found on one-use cameras and other cheap 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 focus by means of a coupled parallax unit on top of the camera. 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. 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 which stores images onto magnetic tape (either using analogue or digital technology). Stereo camera can take photographs that appear "three-dimensional" by taking two different photographs which are combined to create the illusion of depth in the composite image. Stereo cameras for making 3D prints or slides have two lenses side by side. Stereo cameras for making lenticular prints have 3, 4, 5, or even more lenses. Some film cameras feature date imprinting devices that can print a date on the negative itself.

History

date imprinting date imprinting 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. However, while this was the birth of photography, the camera itself can be traced back much further. Photographic cameras were a development of the camera obscura, a device dating back at least to the 11th century which uses a pinhole or lens to project an image of the scene outside onto a viewing surface. Before the invention of photography, there was no way to preserve the images produced by these cameras apart from manually tracing them. 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 possible. 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 Talbot recorded images on paper. 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 wet-plate 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 sophisticate 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 making cartes de visite. It was during the wet plate era that the use of bellows for focusing became widespread.

Camera brands

- Agfa
- ARCA-Swiss
- Agilux
- Balda
- Bolex
- Braun
- Bronica
- Burke & James
- Cambo
- Canon
- Casio
- Contax
- Corfield
- Coronet
- Ebony
- FED
- Fujifilm
- Graflex
- Hasselblad
- Hewlett Packard
- Ilford
- Kodak
- Konica
- Leica
- Linhof
- Lomo
- Minolta
- Mamiya
- Minox
- MPP
- Newman & Guardia
- Nikon
- Olympus
- Osaka
- Panasonic
- Pentax
- Polaroid
- Praktica
- Reid
- Ricoh
- Rollei
- Sigma Corporation
- Sony
- Vivitar
- Voigtländer
- Wisner
- Wray
- Yashica
- Zeiss
- Zenit
- Zone VI
- Zorki

External links

- [http://www.camerapedia.org/wiki/Main_Page Camerapedia: a free-content encyclopedia of camera information]
- [http://www.sankey.ws/pinhole.html Pinhole camera for tree photography] Category:Photography Category:Photographic equipment ko:사진기 ja:カメラ

Camera

Description

History

Camera brands

External links

Photographs

:Photo redirects here. For the French magazine, see Photo (magazine). A photograph (often shortened to photo) is an image (or a representation of that on e.g. paper) created by collecting and focusing reflected electromagnetic radiation. The most common photographs are those created of reflected visible wavelengths, producing permanent records of what the human eye can see. Most photographs are made with a camera, which focuses the light onto either photographic film or a CCD or CMOS image sensor. Photographs can also be made by placing objects on photosensitive paper and exposing it to light (the result is often called a photogram) or by placing objects on the platen of a flatbed scanner (see scanner art).

History and special effects

Most traditional photographs are produced with a two-step chemical process. In the two-step process, the film holds a negative image (colours and lights/darks are inverted), which is then transferred onto photographic paper as a positive image. Another widely used film is the positive film used for producing transparencies, usually mounted in cardboard or plastic frames called slides. Slides are widely used by professionals mostly due to their sharpness and accuracy of colour rendition. Most photographs published in magazines are still originally taken on colour transparency film. transparencies Originally almost all photographs were black and white. Although methods for developing color photos were available as early as the late 19th century, they did not become widely available until the 1940s or 50s, and even in until the 1960s most photographs were taken in black and white. Since then, color photography has dominated popular photography, although the black and white format remains popular for amateur photographers and artists. Black and white film is considerably easier to develop than colour. Panoramic format Images can be taken by using special cameras like the Hasselblad Xpan on standard film. Since the 1990s, panoramic photos have been relatively easy for the general population to take on Advanced Photo System film. APS was developed by several of the major film manufacturers to provide a "smart" film with different formats and computerized options available, though APS panoramas were created using a mask in panorama-capable cameras, far less desirable than a true panoramic camera which achieves its effect through wider film format. As with many past ideas in consumer film formats, APS has become less popular and will be discontinued in the near future. Digital photos can be stored in various file formats, of which JPEG is one of the most popular. Many other graphic formats are used, including TIFF, PNG, GIF, and RAW.

Video camera

A video camera can be classified three ways:
- Professional video cameras, such as those used in television production
- Camcorders used by amateurs
- Closed-circuit television used for surveillance

Latin

Latin is an ancient Indo-European language originally spoken in the region around Rome called Latium. It gained great importance as the formal language of the Roman Empire. All Romance languages, those being most notably Spanish, French, Portuguese, Italian, and Romanian, are descended from Latin, and many words based on Latin are found in other modern languages such as English. The Latin alphabet, derived from the Greek, remains the most widely-used alphabet in the world. It is said that 80 percent of scholarly English words are derived from Latin (in a large number of cases by way of French). Moreover, in the Western world, Latin was a lingua franca, the learned language for scientific and political affairs, for more than a thousand years, being eventually replaced by French in the 18th century and English in the late 19th. Ecclesiastical Latin remains the formal language of the Roman Catholic Church to this day, and thus the official national language of the Vatican. The Church used Latin as its primary liturgical language until the Second Vatican Council in the 1960s. Latin is also still used (drawing heavily on Greek roots) to furnish the names used in the scientific classification of living things. The modern study of Latin, along with Greek, is known as Classics.

Main features

Latin is a synthetic inflectional language: affixes (which usually encode more than one grammatical category) are attached to fixed stems to express gender, number, and case in adjectives, nouns, and pronouns, which is called declension; and person, number, tense, voice, mood, and aspect in verbs, which is called conjugation. There are five declensions (declinationes) of nouns and four conjugations of verbs. There are six noun cases: #nominative (used as the subject of the verb or the predicate nominative), #genitive (used to indicate relation or possession, often represented by the English of or the addition of s to a noun), #dative (used of the indirect object of the verb, often represented by the English to or for), #accusative (used of the direct object of the verb, or object of the preposition in some cases), #ablative (separation, source, cause, or instrument, often represented by the English by, with, from), #vocative (used of the person or thing being addressed). In addition, some nouns have a locative case used to express location (otherwise expressed by the ablative with a preposition such as in), but this survival from Proto-Indo-European is found only in the names of lakes, cities, towns, small islands, and a few other words related to locations, such as "house", "ground", and "countryside". Latin itself, being a very old language, is far closer to Proto-Indo-European than are most modern Western European languages; it has, in fact, about the same relationship with PIE as modern Italian or French has to Latin. There are six general tenses in Latin (technically they are tense/aspect/mood complexes). The indicative mood can be used with all of them. The subjunctive mood, however, has only present, imperfect, perfect, and pluperfect tenses. These tenses in the subjunctive mood do not completely correlate in meaning to the tenses in the indicative. The following examples are of the first conjugation verb "laudare" ("to praise") in the indicative mood and the active voice:
Primary sequence tenses
# present (laudo, "I praise") # imperfect (laudabam, "I was praising") # future (laudabo, "I shall praise," "I will praise")
Secondary sequence tenses
# perfect (laudavi, "I praised", "I have praised") # pluperfect (laudaveram, "I had praised") # future perfect (laudavero, "I shall have praised," "I will have praised") The future perfect tense can also imply a normal future idea (like in "When I will have run...") and so may also sometimes be included in the primary sequence.
Latin and Romance
After the collapse of the Roman Empire, Latin evolved into the various Romance languages. These were for many centuries only spoken languages, Latin still being used for writing. For example, Latin was the official language of Portugal until 1296 when it was replaced by Portuguese. The Romance languages evolved from Vulgar Latin, the spoken language of common usage, which in turn evolved from an older speech which also produced the formal classical standard. Latin and Romance differ (for example) in that Romance had distinctive stress, whereas Latin had distinctive length of vowels. In Italian and Sardo logudorese, there is distinctive length of consonants and stress, in Spanish only distinctive stress, and in French even stress is no longer distinctive. Another major distinction between Romance and Latin is that all Romance languages, excluding Romanian, have lost their case endings in most words except for some pronouns. Romanian retains a direct case (nominative/accusative), an indirect case (dative/genitive), and vocative. In Italy, Latin is still compulsory in secondary schools as Liceo Classico and Liceo Scientifico which are usually attended by people who aim to the highest level of education. In Liceo Classico Ancient Greek is a compulsory subject.
Latin and English
See Latin influence in English for a more complete exposition. English grammar is independent of Latin grammar, though prescriptive grammarians in English have been heavily influenced by Latin. Attempts to make English grammar follow Latin rules — such as the prohibition against the split infinitive — have not worked successfully in regular usage. However, as many as half the words in English were derived from Latin, including many words of Greek origin first adopted by the Romans, not to mention the thousands of French, hundreds of Spanish, Portuguese and Italian words of Latin origin that have also enriched English. During the 16th and on through the 18th century English writers created huge numbers of new words from Latin and Greek roots. These words were dubbed "inkhorn" or "inkpot" words (as if they had spilled from a pot of ink). Many of these words were used once by the author and then forgotten, but some remain. Imbibe, extrapolate, dormant and inebriation are all inkhorn terms carved from Latin words. In fact, the word etymology is derived from the Greek word etymologia, meaning "true sense of the word." Latin was once taught in many of the schools in Britain with academic leanings - perhaps 25% of the total [http://www.channel4.com/history/microsites/T/teachem2/thennow/]. However, the requirement for it was gradually abandoned in the professions such as the law and medicine, and then, from around the late 1960s, for admission to university. After the introduction of the Modern Language GCSE in the 1980s, it was gradually replaced by other languages, although it is now being taught by more schools along with other classical languages.
Latin education
The linguistic element of Latin courses offered in high schools or secondary schools, and in universities, is primarily geared toward an ability to translate Latin texts into modern languages, rather than using it in oral communication. As such, the skill of reading is heavily emphasized, whereas speaking and listening skills are barely touched upon. However, there is a growing movement, sometimes known as the Living Latin movement, whose supporters believe that Latin can, or should, be taught in the same way that modern "living" languages are taught, that is, as a means of both spoken and written communication. One of the most interesting aspects of such an approach is that it assists speculative insight into how many of the ancient authors spoke and incorporated sounds of the language stylistically; without understanding how the language is meant to be heard it is very difficult to identify patterns in Latin poetry. Institutions offering Living Latin instruction include the Vatican and the University of Kentucky. In Britain the Classical Association encourages this approach, and there has been something of a vogue for books describing the adventures of a mouse called Minimus. In the United States there is a thriving competitive organization for high school Latin students, the National Junior Classical League (the second-largest youth organization in the world after the Boy Scouts), backed up by the Senior Classical League for college students. Many would-be international auxiliary languages have been heavily influenced by Latin, and the moderately successful Interlingua considers itself to be the modernized and simplified version of the language (le latino moderne international e simplificate). Latin translations of modern literature such as Paddington Bear, Winnie the Pooh, Harry Potter and the Philosopher's Stone, Le Petit Prince, Max und Moritz, and The Cat in the Hat have also helped boost interest in the language.
See also

About the Latin language

- Latin grammar
- Latin spelling and pronunciation
- Latin declension
- Latin conjugation
- Latin alphabet
- List of Latin words with English derivatives
- Latin verbs with English derivatives
- Latin nouns with English derivatives
- ablative absolute
- Word order in Latin
About the Latin literary heritage

- Latin literature
- Romance languages
- Loeb Classical Library
- List of Latin phrases
- List of Latin proverbs
- Brocard
- List of Latin and Greek words commonly used in systematic names
- List of Latin place names in Europe
- Carmen Possum
Other related topics

- Roman Empire
- Internationalism
References

- Bennett, Charles E. Latin Grammar (Allyn and Bacon, Chicago, 1908)
- N. Vincent: "Latin", in The Romance Languages, M. Harris and N. Vincent, eds., (Oxford Univ. Press. 1990), ISBN 0195208293
- Waquet, Françoise, Latin, or the Empire of a Sign: From the Sixteenth to the Twentieth Centuries (Verso, 2003) ISBN 1859844022; translated from the French by John Howe.
- Wheelock, Frederic. Latin: An Introduction (Collins, 6th ed., 2005) ISBN 0060784237
External links

- [http://www.jambell.com/latin.html Latin Phrases for after dinner conversation (Thanks to Elaine Poole)]
- [http://www.ethnologue.com/show_language.asp?code=lat Ethnologue report for Latin]
- [http://forumromanum.org/literature/index.html Corpus Scriptorum Latinorum] is a comprehensive webography of Latin texts and their translations.
- [http://www.perseus.tufts.edu/ The Perseus Project] has many useful pages for the study of classical languages and literatures, including [http://www.perseus.tufts.edu/cgi-bin/resolveform?lang=Latin an interactive Latin dictionary].
- [http://lysy2.archives.nd.edu/cgi-bin/words.exe words by William whitaker] is a dictionary program online capable of looking up various word forms.
- [http://retiarius.org/ Retiarius.Org] includes a Latin text search engine.
- [http://www.nd.edu/~archives/latgramm.htm Latin-English dictionary and Latin grammar from U of Notre Dame]
- [http://latin-language.co.uk/ Latin language] History of Latin language, Latin texts with English translation and a collection of dictionaries.
- [http://augustinus.eresmas.net/scl/ Societas Circulorum Latinorum] gathers together Latin Circles all over the world.
- [http://www.learnlatin.tk LearnLatin.tk] - Free online course in Latin
- [http://www.latintests.net/ LatinTests.net] - Lets Latin learners test their grammar and vocabulary with self-checking quizzes.
- [http://thelatinlibrary.com/ The Latin Library] contains many Latin etexts
- [http://www.textkit.com/ Textkit] has Latin textbooks and etexts.
- [http://www.websters-online-dictionary.org/definition/Latin-english/ Latin–English Dictionary]: from Webster's Rosetta Edition.
- [http://www.language-reference.com/ Language reference] Cross-foreign-language lexicon powered by its own search engine. All cross combinations between Latin and French, German, Italian, Spanish.
- [http://comp.uark.edu/~mreynold/rhetor.html Rhetor by Gabriel Harvey] was originally published in 1577 and never again reprinted.
- [http://freewebs.com/omniamundamundis omniamundamundis] Latin hypertexts from fourteen ancient Roman authors.
- [http://www.saltspring.com/capewest/pron.htm Pronunciation of Biological Latin, Including Taxonomic Names of Plants and Animals]
- [http://www.yleradio1.fi/nuntii Nuntii Latini (News in Latin)], written and spoken (RealAudio) news in latin. Weekly review of world news in Classical Latin, the only international broadcast of its kind in the world, produced by YLE, the Finnish Broadcasting Company.
- [http://www.tranexp.com:2000/InterTran?url=http%3A%2F%2F&type=text&text=Replace%20Me&from=eng&to=ltt InterTran Latin], Translate from Latin to ENGLISH or vice versa.
- [http://www.latinvulgate.com Latin Vulgate] The Latin and English of the Old & New Testaments in parallel, along with the Complete Sayings of Jesus in parallel Latin and English. Category:Classical languages Category:Ancient languages Category:Fusional languages Category:Languages of Italy Category:Languages of Vatican City als:Latein zh-min-nan:Latin-gí ko:라틴어 ja:ラテン語 simple:Latin language th:ภาษาละติน

Visual spectrum

The visible spectrum is the portion of the optical spectrum (light or electromagnetic spectrum) that is visible to the human eye. There are no exact bounds to the optical spectrum, but there are to the visible spectrum. A typical human eye will respond to wavelengths from 400 to 700 nm, although some people may be able to perceive wavelengths from 380 to 780 nm. A light-adapted eye typically has its maximum sensitivity at around 555 nm, in the green region of the optical spectrum. Wavelengths visible to the eye also pass through the "visible window", the region of the electromagnetic spectrum which passes largely unattenuated through the Earth's atmosphere (although blue light is scattered more than red light, which is the reason the sky is blue). The response of the human eye is defined by subjective testing (see CIE), but the atmospheric windows are defined by physical measurement. The "visible window" is so called because it overlaps the human visible response spectrum; the near infrared (NIR) windows lie just out of human response window, and the Medium Wavelength IR (MWIR) and Long Wavelength or Far Infrared (FIR or LWIR) are far beyond the human response region. The eyes of many species perceive wavelengths different than the spectrum visible to the human eye. For example, many insects, such as bees, can see light in the ultraviolet, which is useful for finding nectar in flowers. flower into the colors of the optical spectrum.]]

Historical use of the term

Sir Isaac Newton first used the word spectrum (Latin for "appearance" or "apparition") in print in 1671 in describing his experiments in optics. Newton observed that, when a narrow beam of white sunlight strikes the face of a glass prism at an angle, some is reflected and some of the beam passes into and through the glass, emerging as different colored bands. Newton hypothesized that light was made up of "corpuscles" (particles) of different colors, and that the different colors of light moved at different speeds in transparent matter, with red light moving more quickly in glass than violet light. The result is that red light was bent (refracted) less sharply that violet light as it passed through the prism, creating a spectrum of colors. It is now known light is composed of photons (which display some of the properties of a wave and some of the properties of a particle), and that all light travels at the same speed (the speed of light) in a vacuum. The speed of light within a material is lower than the speed of light in a vacuum, and the ratio of speeds is known as the refractive index of the material. In some materials, known as non-dispersive, the speed of different frequencies (corresponding to the different colors) does not vary, and so the refractive index is a constant. However, in other (dispersive) materials, the refractive index (and thus the speed) depends on frequency in accorance with a dispersion relation: glass is one such material, which enables glass prisms to create an optical spectrum from white light.

Spectroscopy

dispersion relation transmittance (or opacity) to various wavelengths of electromagnetic radiation, including visible light.]] The scientific study of objects based on the spectrum of the light they emit is called spectroscopy. One particularly important application of spectroscopy is in astronomy, where spectroscopy is essential for analysing the properties of distant objects. Typically, astronomical spectroscopy utilises high-dispersion diffraction gratings to observe spectra at very high spectral resolutions. Helium was first detected through an analysis of the spectrum of the Sun; chemical elements can be detected in astronomical objects by emission lines and absorption lines; and the shifting of spectral lines can be used to measure the redshift or blueshift of distant or fast-moving objects. The first exoplanets to be discovered were found by analysing the doppler shift of stars at such high resolution that variations in their radial velocity as small as a few metres per second could be detected: the presence of planets was revealed by their gravitational influence on the motion of the stars analysed.

Electromagnetic spectrum

s
SX = Soft X-Rays
EUV = Extreme ultraviolet
NUV = Near ultraviolet
Visible light
NIR = Near infrared
MIR = Moderate infrared
FIR = Far infrared

Radio waves:
EHF = Extremely high frequency (Microwaves)
SHF = Super high frequency (Microwaves)
UHF = Ultrahigh frequency
VHF = Very high frequency
HF = High frequency
MF = Medium frequency
LF = Low frequency
VLF = Very low frequency
VF = Voice frequency
ELF = Extremely low frequency]] The electromagnetic spectrum is the range of all possible electromagnetic radiation. Also, the "electromagnetic spectrum" (usually just spectrum) of an object is the range of electromagnetic radiation that it emits, reflects, or transmits. The electromagnetic spectrum, shown in the table, extends from frequencies used in the electric power grid (at the long-wavelength end) to gamma radiation (at the short-wavelength end), covering wavelengths from thousands of kilometres down to fractions of the size of an atom, though in principle the spectrum is actually infinite. Electromagnetic energy at a particular wavelength λ (in vacuum) has an associated frequency ν and photon energy E. Thus, the electromagnetic spectrum may be expressed equally well in terms of any of these three quantities. They are related according to the equations: :

\lambda = \frac  \,\!

and :

E=h\nu \,\!

where:
- c is the speed of light, 299792458 m/s

(c \approx 3 \cdot 10^8 \ \mbox/\mbox = 300,000 \ \mbox/\mbox)

.
- h is Planck's constant,

(h \approx 6.626069 \cdot 10^ \ \mbox \cdot \mbox \approx 4.13567 \ \mathrm \mbox/\mbox)

Spectra of objects

Nearly all objects in the universe emit, reflect and/or transmit some light. The distribution of this light along the electromagnetic spectrum (called the spectrum of the object) is determined by the object's composition. Several types of spectra can be distinguished depending upon the nature of the radiation coming from an object:
- If the spectrum is composed primarily of thermal radiation emitted by the object itself, an emission spectrum occurs.
- Some bodies emit light more or less according to the blackbody spectrum.
- If the spectrum is composed of background light, parts of which the object transmits and parts of which it absorbs, an absorption spectrum occurs. Electromagnetic spectroscopy is the branch of physics that deals with the characterization of matter by its spectra.

Classification systems

While the classification scheme is generally accurate, in reality there is often some overlap between neighboring types of electromagnetic energy. For example, SLF radio waves at 60 Hz may be received and studied by astronomers, or may be ducted along wires as electric power. Also, some low-energy gamma rays actually have a longer wavelength than some high-energy X-rays. This is possible because "gamma ray" is the name given to the photons generated from nuclear decay or other nuclear and subnuclear processes, whereas X-rays on the other hand are generated by electronic transitions involving highly energetic inner electrons. Therefore the distinction between gamma ray and X-ray is related to the radiation source rather than the radiation wavelength. Generally, nuclear transitions are much more energetic than electronic transitions, so usually, gamma-rays are more energetic than X-rays. However, there are a few low-energy nuclear transitions (e.g. the 14.4 keV nuclear transition of Fe-57) that produce gamma rays that are less energetic than some of the higher energy X-rays. Use of the radio frequency spectrum is regulated by governments. This is called frequency allocation.

Electric energy

Electrical energy covers the low-frequency, long-wavelength end of the spectrum. The radiation is usually ducted along 2-wire and 3-wire transmission lines and sent to various devices besides antennas. At zero frequency the energy is emitted by batteries and DC power supplies, while at 50 Hz and 60 Hz it is produced by rotary magnetic generators and ducted through the international power grids. At frequencies between 20 Hz to 30 kHz the EM energy is translated to and from acoustic energy and is distributed over telephone lines, as well as being used to operate loudspeakers for public address or in music systems. Note that other than its frequency, there is no functional difference between the VHF energy guided along a television coaxial cable, versus the 60 Hz travelling along the cord leading to a light bulb. When connected to the appropriate antenna, both will radiate into space.

Radio frequency

telephone lines Radio waves generally are utilized by antennas of appropriate size, with wavelengths ranging from hundreds of meters to about one millimeter. They are used for transmission of data, via modulation. Television, mobile phones, wireless networking and amateur radio all use radio waves.

Microwaves

The super high frequency (SHF) and extremely high frequency (EHF) of Microwaves come next. Microwaves are waves which are typically short enough to employ tubular metal waveguides of reasonable diameter. Microwave energy is produced with klystron and magnetron tubes, and with solid state diodes such as Gunn and IMPATT devices. Microwaves are absorbed by molecules that have a dipole moment in liquids. In a microwave oven, this effect is used to heat food. Low-intensity microwave radiation is used in Wi-Fi. It should be noted that an average microwave oven in active condition is, in close range, powerful enough to cause interference with poorly shielded electromagnetic fields such as those found in mobile medical devices and cheap consumer electronics.

Terahertz radiation

This is a region of the light spectrum between far infrared and microwaves. Until recently, the range was rarely studied and few sources existed for microwave energy at the high end of the band (sub-millimeter waves or so-called terahertz waves), but applications are now appearing. The proposed WiMAX standard for wireless networking, a long-range enhancement of Wi-Fi, lies within this region. Scientists are also looking to apply Terahertz technology in the armed forces, where high frequency waves will be sent at enemy troops to incapacitate them.

Infrared radiation

The infrared part of the electromagnetic spectrum covers the range from roughly 300 GHz (1 mm) to 400 THz (750 nm). It can be divided into three parts:
- Far-infrared, from 300 GHz (1 mm) to 30 THz (10 μm). The lower part of this range may also be called microwaves. This radiation is typically absorbed by so-called rotational modes in gas-phase molecules, by molecular motions in liquids, and by phonons in solids. The water in the Earth's atmosphere absorbs so strongly in this range that it renders the atmosphere effectively opaque. However, there are certain wavelength ranges ("windows") within the opaque range which allow partial transmission, and can be used for astronomy. The wavelength range from approximately 200 μm up to a few mm is often referred to as "sub-millimeter" in astronomy, reserving far infrared for wavelengths below 200 μm.
- Mid-infrared, from 30 to 120 THz (10 to 2.5 μm). Hot objects (black-body radiators) can radiate strongly in this range. It is absorbed by molecular vibrations, that is, when the different atoms in a molecule vibrate around their equilibrium positions. This range is sometimes called the fingerprint region since the mid-infrared absorption spectrum of a compound is very specific for that compound.
- Near-infrared, from 120 to 400 THz (2,500 to 750 nm). Physical processes that are relevant for this range are similar to those for visible light.

Visible radiation (light)

Color	Wavelength interval	Frequency interval
violet	~ 380 to 430 nm	~ 790 to 700 THz
blue	~ 430 to 500 nm	~ 700 to 600 THz
cyan	~ 500 to 520 nm	~ 600 to 580 THz
green	~ 520 to 565 nm	~ 580 to 530 THz
yellow	~ 565 to 590 nm	~ 530 to 510 THz
orange	~ 590 to 625 nm	~ 510 to 480 THz
red	~ 625 to 740 nm	~ 480 to 405 THz
Continuous spectrum Image:Spectrum441pxWithnm.png The spectrum of visible light Designed for monitors with gamma 1.5.

After infrared comes visible light. This is the range in which the sun and stars similar to it emit most of their radiation. It is probably not a coincidence that the human eye is sensitive to the wavelengths that the sun emits most strongly. Visible light (and near-infrared light) is typically absorbed and emitted by electrons in molecules and atoms that move from one energy level to another. The light we see with our eyes is really a very small portion of the electromagnetic spectrum. A rainbow shows the optical (visible) part of the electromagnetic spectrum; infrared (if you could see it) would be located just beyond the red side of the rainbow with ultraviolet appearing just beyond the violet end.

Ultraviolet light

Next comes ultraviolet. This is radiation whose wavelength is shorter than the violet end of the visible spectrum. Being very energetic, UV can break chemical bonds, make molecules unusually reactive or ionize them, in general changing their mutual behavior. Sunburn, for example, is caused by the disruptive effects of UV radiation on skin cells, which can even cause skin cancer, if the radiation damages the complex DNA molecules in the cells (UV radiation is a proven mutagen). The Sun emits a large amount of UV radiation, which could quickly turn Earth into a barren desert, but most of it is absorbed by the atmosphere's ozone layer before reaching the surface.

X-rays

After UV come X-rays. Hard X-rays are of shorter wavelengths than soft X-rays. X-rays are used for seeing through some things and not others, as well as for high-energy physics and astronomy. Neutron stars and accretion disks around black holes emit X-rays, which enable us to study them.

Gamma rays

After hard X-rays come gamma rays. These are the most energetic photons, having no lower limit to their wavelength. They are useful to astronomers in the study of high-energy objects or regions and find a use with physicists thanks to their penetrative ability and their production from radioisotopes. The wavelength of gamma rays can be measured with high accuracy by means of Compton scattering. Note that there are no defined boundaries between the types of electromagnetic radiation. Some wavelengths have a mixture of the properties of two regions of the spectrum. For example, red light resembles infra-red radiation in that it can resonate some chemical bonds.

External links

- [http://www.ntia.doc.gov/osmhome/allochrt.html U.S. Frequency Allocation Chart] - Covering the range 3 kHz to 300 GHz (from Department of Commerce)
- [http://strategis.ic.gc.ca/epic/internet/insmt-gst.nsf/vwapj/spectallocation.pdf/%24FILE/spectallocation.pdf Canadian Table of Frequency Allocations] (from Industry Canada)
- [http://www.ofcom.org.uk/static/archive/ra/topics/spectrum-strat/future/strat02/strategy02app_b.pdf UK frequency allocation table] (from Ofcom, which inherited the Radiocommunications Agency's duties, pdf format)
- [http://www.scienceofspectroscopy.info The Science of Spectroscopy] - supported by NASA, includes OpenSpectrum, a Wiki-based learning tool for spectroscopy that anyone can edit
- [http://www.e-builds.com/EM%20spectrum/ An EM Spectrum Overview in Flash] by e-builds ja:電磁スペクトル

Aperture

In optics, an aperture is something which restricts the diameter of the light path through one plane in an optical system. This may be the edge of a lens or mirror, or a ring or other fixture that holds an optical element in place, or it may be a special element placed in the optical path deliberately to limit the light admitted by the system. The aperture stop or simply the stop is the limiting aperture of the system—the aperture which restricts the diameter of the cone or cylinder of light that can enter and pass through the system. The diameter of the aperture stop is sometimes simply referred to as the aperture of the system, especially when speaking of cameras and telescopes. Note that the aperture stop is not necessarily the smallest aperture in the system. Magnification and demagnification by lenses and other elements can cause a relatively large aperture to be the stop for the system.

Application

The aperture stop is an extremely important element in most optical designs. Its most obvious function is to reduce the amount of light that can reach the image plane, to prevent saturation of a detector or overexposure of film. The aperture stop has far more important functions, however:
- The size of the stop determines the depth of field of the system. Smaller stops produce a longer depth of field, allowing objects at a wide range of distances to all be in focus at the same time.
- The stop limits the effect of optical aberrations. If the stop is too large, the image will be distorted. More sophisticated optical system designs can mitigate the effect of aberrations, allowing a larger stop and therefore greater light collecting ability.
- The stop determines the system's field of view.
- The stop determines whether the image will be vignetted. Larger stops cause the intensity reaching the film or detector to fall off toward the edges of the picture. The pupil of the eye is its aperture stop. Refraction in the cornea causes the effective aperture (the entrance pupil) to differ slightly from the physical pupil diameter. The entrance pupil is typically about 4 mm in diameter, although it can range from 2 mm (f/8.3) in a brightly lit place to 8 mm (f/2.1) in the dark.

In photography

The aperture stop of a photographic lens can be adjusted to control the amount of light reaching the film or digital sensor (CCD or CMOS). In combination with variation of shutter speed and film speed, the aperture size will regulate the film's degree of exposure to light. Typically, a fast shutter speed will require a larger aperture to ensure sufficient light exposure, and a slow shutter speed will require a smaller aperture to avoid excessive exposure. A device called a diaphragm controls the aperture. The diaphragm can be considered to function much like the pupil of the eye—it controls the effective diameter of the lens opening. Reducing the aperture size increases the depth of field, which describes the extent to which subject matter lying closer than or farther from the actual plane of focus appears to be in focus. In general, the smaller the aperture (the larger the number), the greater the distance from the plane of focus the subject matter may be while still appearing in focus. depth of field Aperture is usually measured in f-numbers. A lens will have a set of "f-stops" that represent doublings in the amount of light let through the aperture. A lower f-stop number denotes a greater aperture opening which allows more light to reach the film. A typical standard lens will have an f-stop range from f/16 (small aperture) to f/2 (large aperture). Professional lenses can have f-stops as low as f/1.0 (very large aperture). These are known as "fast" lenses because they allow much more light to reach the film and therefore reduce the required exposure time. Large aperture prime lenses (lenses which have a fixed focal length) are favored especially by photojournalists who often work in dim light, have no opportunity to introduce supplementary lighting, and capture fast breaking events. Zoom lenses typically go from f/2.8 to f/6.3. A very fast zoom lens will be constant f/2.8, which means the aperture will stay the same throughout the zoom range. A normal zoom will be a constant f/4, and a consumer zoom will typically have a variable diaphragm, normally being something along the lines of f/4.5 to f/5.6, or even f/4.5 to f/6.3 (rare). There are a few exceptions to this rule, as even high quality hyperzooms often have as slow of an aperture as f/5.6 throughout the whole zoom range. Such is the case with most lenses which have more than 4x zoom range, like a 100-400 mm f/5.6. The reason for consumer zooms to have a variable aperture is that the f-number is proportional to the ratio of the focal length to the diameter of the diaphragm opening. This means that if you have a 75-300 mm lens, a physically bigger diaphragm opening will be needed at 300 mm than at 75 mm, to maintain the same f-number. More light is needed as the focal length increases, to compensate for the fact that light from a smaller field of view is being spread over the same area of film or detector.

Maximum and minimum apertures

The specifications for a given lens might include the minimum and maximum apertures. These refer to the maximum and minimum f-numbers the lens can be set at to achieve, respectively, the minimum and maximum input of light. For example, the Canon EF 70-200mm lens has a maximum aperture of f/2.8 and a minimum aperture of f/32. This may seem counterintuitive since the maximum aperture has a smaller number while the minimum aperture has a larger number, but makes sense since the smaller number corresponds to a physically larger aperture opening. This can be remembered by thinking of the f/numbers as fractions and recalling that 1/2.8 is greater than 1/32. It should be noted that the maximum aperture tends to be of most interest (makes it easier to shoot under dim lighing conditions because the lens lets more light through to the film or CCD) and is usually included when describing a lens (e.g., 100-400mm f/5.6, 70-200mm f/2.8). The minimum aperture is useful for time-lapse pictures shot on film (it places an upper limit on the exposure time for a given lighting condition) and maximum depth of field.

References

External links

- [http://www.kevinwilley.com/l3_topic02.htm Aperture size, and its effect on depth of field]
- [http://www.kevinwilley.com/l3_topic01.htm Derivation of the f-stop numbers that identify aperture sizes] Category:Photographic terms Category:Optics ja:絞り (光学)

Diaphragm (optics)

al diaphragm opening is 4.375mm]] In optics, a diaphragm is an opening in the lightpath of a lens or objective that can regulate the amount of light that passes. The centre of the diaphragm coincides with the optical axis of the lens system. Normally it is shaped in a near-round fashion by a number of curved blades. Diaphragms usually have five to eight blades, depending on the intended uses, pricing and quality of the device in which it is used. Many cameras have an adjustable diaphragm to control the amount of light, which can also be regulated by adjusting the shutter time. The principle is identical to that of the iris in the human eye. A small diaphragm reduces the amount of light, but also reduces the influence of aberrations of the optical lens system and increases the depth of field. The reduced light intensity will however require the shutter time to be increased, which leads to increased blurring if the subject of the photograph or the camera moves during the exposure. The number of blades in a diaphragm has a direct relation with the appearance of the blurred out-of-focus areas in an image, also called Bokeh. The more blades a diaphragm has, the rounder and less polygon-shaped the opening will be. This results in softer and more gradually blurred out-of-focus areas. In a picture, the number of blades the diaphragm used has, can be guessed by counting the number of spikes converging from a light source or bright reflection. There are always twice as many spikes as there are blades. In case of an even number of blades, these spikes will overlap each other, so the number of spikes visible will be the number of spikes in de diaphragm used. This is most apparent in pictures taken in the dark with small bright spots, for example nightly cityscapes.

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 the right amount of light to create a permanent image of a view. Shutters are normally of two basic types:
- Shutters mounted within a lens central shutters, or more rarely behind or even in front of a lens
- Shutters fitted near the focal plane Shutters of the first type usually have a a diaphragm-like mechanism which progressively dilate to a circular opening the size of the lens, then stay open as long as is required, and finally close. Ideally the opening and closing are instantaneous; in reality this cannot be so. The time taken to dilate, and then to contract, places a lower limit on the exposure time. A less obvious property is that at the highest speeds the shutter is fully open for only a fraction of the exposure; the effective aperture is less, and the depth of field greater, than at lower speeds. Shutters immediately behind the lens were used in some cameras with limited lens interchangeability. Shutters in front of the lens were used in the early days of photography. Focal-plane shutters are usually implemented as a pair of cloth, metal, or plastic curtains which shield the film from light. For exposures of, typically, 1/30th of a second or more, one curtain opens, and the second one later closes. For shorter exposures, the two curtains move simultaneously, but leaving a slit-shaped opening through which light can pass. The speed of motion of the curtains and the width of the slit are adjusted so that each part of the film is exposed to light for the required time (the effective exposure), although the assembly may take an appreciable time (typically 1/30") to traverse the film. The effective exposure time can be much shorter than for central shutters. Focal plane shutters have the advantages of enabling much shorter exposures, and allowing the use of interchangeable lenses without requiring the expense of a separate shutter for each lens. They have the disadvantage of distorting the images of fast-moving objects: although no part of the film is exposed for longer than the time set on the dial, one edge of the film is exposed an appreciable time after the other, so that a horizontally moving shutter will, for example, elongate or shorten the image of a car speeding in the same or the opposite direction to the shutter movement. Other mechanisms than the dilating aperture and the sliding curtains have been used; anything which exposes the film to light for a specified time will suffice. The time for which a shutter remains open, the exposure time, is determined by a timing mechanism. These were originally mechanical, but since the late twentieth century are mostly electronic. The exposure time and the effective aperture of the lens must together be such as to allow the right amount to reach the film or sensor. Additionally, the exposure time must be suitable to handle any motion of the subject. Usually it must be fast enough to "freeze" rapid motion; sometimes a controlled degree of blur is desired, to give a sensation of movement. Most shutters generate a signal to trigger a flash, if connected. This was quite a complicated matter with mechanical shutters and flashbulbs which took an appreciable time to reach full brightness, but is simple with electronic timers and electronic flash units which fire virtually instantaneously. Cinematography uses a rotary disc shutter in movie cameras, a continuously spinning disc which conceals the image with a reflex mirror during the intermittent motion between frame exposure. The disc then spins to an open section that exposes the next frame of film while it is held by the registration pin. In movie projection, the shutter admits light from the lamphouse to illuminate the film across to the projection screen. To avoid flicker, a double-bladed rotary disc shutter admits light 2 times each frame of film. There are also some models which are triple bladed, and thus do this and 3 times per frame (see Persistence of vision).

Shutter speed

settings can achieve unusual results]] In photography, shutter speed is the time for which the shutter is held open during the taking of a photograph to allow light to reach the film or imaging sensor (in a digital camera). In combination with variation of the lens aperture, this regulates how exposed the film will be or how much light the imaging sensor in a digital camera will receive. For a given exposure, a fast shutter speed demands a larger aperture to avoid under-exposure, just as a slow shutter speed is offset by a very small aperture to avoid over-exposure. Long shutter speeds are often used in low light condition, such as at night. Shutter speed is measured in seconds. A typical shutter speed for photographs taken in sunlight is 1/125th of a second. In addition to its effect on exposure, shutter speed changes the way movement appears in the picture. Very short shutter speeds are used to freeze fast-moving subjects, for example at sporting events. Very long shutter speeds are to intentionally blur a moving subject for artistic effect. In early days of photography, available shutter speeds were somewhat ad hoc. Following the adoption of a standardized way of representing aperture so that each major aperture interval exactly doubled or halved the amount of light entering the camera (f/2.8, f/4, f/5.6, f/8, f/11, f/16 etc.), a standardized 2:1 scale was adopted for shutter speed so that opening one aperture stop and reducing the shutter speed by one step resulted in the identical exposure. The agreed standard for shutter speeds is:
- 1/8000 s
- 1/4000 s
- 1/2000 s
- 1/1000 s
- 1/500 s
- 1/250 s
- 1/125 s
- 1/60 s
- 1/30 s
- 1/15 s
- 1/8 s
- 1/4 s
- 1/2 s
- 1 s
- B (for bulb) — keep the shutter open as long as the release lever is engaged.
- T — keep the shutter open until the lever is pressed again. This scale can be extended at either end in specialist cameras. The ability of the photographer to take images without noticeable blurring by camera movement is an important parameter in the choice of slowest possible shutter speed for a handheld camera. The rough guide used by most 35mm photographers is that the slowest possible shutter speed that can be used with care is the shutter speed numerically closest to the lens focal length. For example, for handheld use of a 35 mm camera with a 50 mm normal lens, the closest shutter speed is 1/60 s. For a free-standing, unsupported photographer it is usually necessary to use the next fastest shutter speed which would be 1/125 s in this case. With great care its possible to use 1/30s with the 50mm lens, or even slower speed especially with non-SLR cameras. Note that using this with "great care" would normally mean bracing the camera, arms, or body to minimise camera movement. If a shutter speed is too slow for hand holding, a camera support—usually a tripod—must be used. Other 35 mm handheld examples are:
- 28 mm wide angle lens, 1/30 s may be used with care, and 1/60 s is advised.
- 105 mm medium telephoto lens, 1/125 s may be used with care, and 1/250 s is advised.
- 300 mm long telephoto lens, 1/250 s may be used with care, and 1/500 s is advised.

Cinematographic Shutter Formulae

In cinematography, shutter speed is a function of the frame rate and shutter angle. Most motion picture film cameras use a rotating shutter with a shutter angle of 170 to 180 °, which leaves the film exposed for about 1/48 or 1/50 second at a standard 24 frame/s. Where E = Exposure, F = Frames per second, and S = Shutter opening: :

E = \frac

S = \frac

See also: exposure, shutter, f-number, exposure value

Additional Photos

Category:Photographic terms

Photographic lens

]] A photographic lens (or more correctly, objective) is an optical lens 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 practice a compound lens made up of a number of optical lens elements is required to correct the many optical aberrations that arise. There is no difference in principle between a lens used for a camera, a telescope, a microscope, or other apparatus, but the detailed design and construction are different. A lens may be permanently fixed to a camera, or it may be interchangeable with lenses of different focal lengths and other properties. A practical camera lens will often incorporate an aperture adjustment mechanism, often an iris diaphragm, to regulate the amount of light that may pass. A shutter, to regulate the time during which light may pass, may be incorporated within the lens assembly, or may be within the camera, or even, rarely, in front of the lens. The lens may usually be focused by adjusting the distance from the lens assembly to the image-forming surface, or by moving elements within the lens assembly. The lens elements are made of transparent materials. Glass is the most widely used material due to its good optical properties and resistance to scratching. Various plastics, such as acrylic (or PMMA), the material of Plexiglas, can also be used. Plastics allow the manufacture of strongly aspherical lens elements which are difficult or impossible to manufacture in glass, and which simplify or improve lens manufacture and performance. Plastics are not used for the outermost elements of all but the cheapest lenses as they scratch easily. Moulded plastic lenses have been used for the cheapest disposable cameras for many years, and have acquired a bad reputation: manufacturers of quality optics tend to use euphemisms such as "optical resin". The maximum usable aperture of a lens is usually specified, as the focal ratio or f-number, the focal length divided by the actual aperture in the same units. The lower the number, the more light is admitted through the lens. Practical lens assemblies may also contain mechanisms to do with measuring light, to hold the aperture open until the instant of exposure to allow SLR cameras to focus with a bright image, etc. The two main optical parameters of a photographic lens are the focal length and the maximum aperture. The focal length determines the angle of view, the size of the image relative to that of the object, and the perspective; the maximum aperture limits the brightness of the image and the fastest shutter speed usable. Focal lengths are usually specifed in millimeters (mm), but older lenses marked in centimeter (cm) and inches are still to be found. For a given film or sensor size, specifed by the length of the diagonal, a lens may be classified as
- Normal lens: angle of view of the diagonal about 50°, the same as the human eye: a focal length approximately equal to the diagonal produces this angle.
- Wide-angle lens: focal length shorter than normal, and angle of view wider.
- Long-focus or telephoto lens: focal length longer than normal, and angle of view narrower. A distinction is sometimes made between a long-focus lens and a true telephoto lens: the telephoto lens is designed to be physically shorter than its focal length. The 35mm film format is so prevalent that a 90mm lens, for example, is always assumed to be a moderate telephoto; but for the 7x5cm format it is normal, while on the large 5x4 inch format it is a wide-angle. The real difference between lenses of different focal length is not the image size, but the perspective. You can take photographs of a person stretching out a hand with a wideangle, a normal lens, and a telephoto, which contain exactly the same image size by changing your distance from the subject. But the perspective will be different. With the wideangle, the hand will be exaggeratedly large relative to the head; as the focal length increases, the emphasis on the outstretched hand decreases. However, if you take pictures from the same distance, and enlarge and crop them to contain the same view, the pictures will be truly identical. A moderate long-focus (telephoto) lens is often recommended for portraiture because the flatter perspective is considered to look more realistic. Some lenses, called zoom lenses, have a focal length which varies as internal elements are moved, typically by rotating the barrel or pressing a button which activates an electric motor. The lens may zoom from moderate wide-angle, through normal, to moderate telephoto; or from normal to extreme telephoto. The zoom range is limited by manufacturing constraints; the ideal of a lens of large maximum aperture which will zoom from extreme wideangle to extreme telephoto is not attainable. Zoom lenses are widely used for small-format cameras of all types: still and cine cameras with fixed or interchangeable lenses. Bulk and price limit their use for larger film sizes. The complexity of a lens—the number of elements and their degree of asphericity—depends upon the angle of view and the maximum aperture. An extreme wideangle lens of large aperture must be of very complex construction to correct for optical aberrations, which are worse at the edge of the field and when the edge of a large lens is used for image-forming. A long-focus lens of small aperture can be of very simple construction to attain comparable image quality; a doublet (with two elements) will often suffice. Some older cameras were fitted with "convertible" lenses of normal focal length; the front element could be unscrewed, leaving a lens of twice the focal length and angle of view, and half the aperture. The simpler half-lens was of adequate quality for the narrow angle of view and small relative aperture. Obviously the bellows had to extend to twice the normal length. Good-quality lenses with maximum aperture no greater than f/2.8 and fixed, normal, focal length need three (triplet) or four elements (the trade name "Tessar" derives from the Greek tessera, meaning "four"). The widest-range zooms often have fifteen or more. The reflection of light at each of the many interfaces between different optical media (air, glass, plastic) seriously degraded the contrast and color saturation of early lenses, zoom lenses in particular, especially where the lens was directly illuminated by a light source. The introduction many years ago of optical coatings, and advances in coating technology over the years, have resulted in major improvements, and modern high-quality zoom lenses give images of quite acceptable contrast.

Special purpose photographic lenses

- Macro lenses are designed for good performance at close distances, e.g., for images of the same size as the object.
- Apochromat lenses have extreme correction for aberrations of colour.
- Process lenses have extreme correction for aberrations of geometry (pincushion distortion, barrel distortion). Process and apochromat lenses are normally of small aperture, and are used for extremely accurate photographs of static objects.
- Enlarger lenses are made to be used with photographic enlargers (specialised projectors), rather than cameras.
- Lenses for aerial photography
- Fisheye lenses: extreme wide-angle lenses with an angle of view of 180 degrees, with very noticeable distortion.
- Stereoscopic lenses, to produce pairs of photographs which give a 3-dimensional effect when viewed with an appropriate viewer.
- Soft-focus lenses which give a soft, but not out-of-focus, image for photographing the vain
- Infrared lenses
- Ultraviolet lenses Some notable photographic optical lens designs are:
- Angenieux retrofocus
- Cooke triplet
- Double-Gauss
- Leitz Elmar
- Rapid Rectilinear
- Zeiss Tessar
- Zeiss Sonnar
- Zeiss Planar Some lens manufacturers (2005):
- Canon
- Cosina
- Konica Minolta
- Leica
- Nikon
- Pentax
- Tamron
- Tokina
- Schneider Kreuznach ([http://www.schneider-kreuznach.com])
- Sigma Corporation
- Zeiss

Scale-focus

Scale-focus or zone-focus is a type of focusing system used by many inexpensive cameras from the 1940s and 1950s. These cameras have an adjustable focus, but lack a focusing aid such as a rangefinder. You had to determine the distance to the subject and set the focus using a scale printed on the lens. If you are good at estimating distances, or have a tape measure at hand, you can get precise, sharp focus with one of these cameras.

Single-lens reflex camera

The single-lens reflex (SLR) is a type of camera that uses a movable mirror placed between the lens and the film to project the image seen through the lens to a matte focusing screen. Most SLRs use a pentaprism to observe the image via an eyepiece, but there are also other finder arrangements, such as the waist-level finder or porro prisms. The shutter in almost all contemporary SLRs sits just in front of the focal plane. If it does not, some other mechanism is required to ensure that no light reaches the film between exposures. For example, the Hasselblad 500C camera uses an auxiliary shutter blind in addition to its in-lens leaf shutter. Since the technology became widespread in the 1970s, SLRs have become the main type of camera used by dedicated amateur photographers and professionals.

Advantages of the SLR

Many of the advantages of SLR cameras derive from viewing the scene through the taking lens. There is no parallax error, and exact focus can be confirmed by eye—otherwise hard for macro photography and when using telephoto lenses. The true depth of field may be seen by stopping down to the taking aperture, possible on all but the cheapest cameras. Because of the SLR's versatility, most manufacturers have a vast range of lenses and accessories available. Only the Leica rangefinder cameras have a comparable system. Compared to most fixed-lens compact cameras, the most commonly used and cheapest SLR lenses offer a wider aperture range and larger maximum aperture (typically f/1.4 to f/1.8 for a 50 mm lens). This allows photographs to be taken in lower light conditions without flash, and allows a narrower depth of field, which is useful for blurring the background behind the subject, which makes the subject stand out better. This is commonly used in portrait photography.

Disadvantages

The most obvious disadvantage of the SLR is its greater weight and size than rangefinders of a similar technology level. The pentaprism and mirror box make the camera body larger. However, rangefinders have not advanced significantly since the 1970s, while modern SLRs use advanced automation and electronics to be smaller and plastics to save weight. The SLR's space-consuming mirror movement makes for difficulty in constructing wide angle lenses; rear lens elements cannot be close to the film plane. Retrofocus designs are required for wide-angle lenses; these are complex, large, and comparatively poorer in image quality. The reflex mirror must retract before the shutter can open, which introduces some delay. Autofocus systems on modern SLRs introduce further delay, especially in lower light. The mirror's movement also causes vibration and noise, a problem when using longer lenses and longer exposures. Technology has reduced but not eliminated this problem, which again is worse in larger formats. To combat this, higher-end cameras offer the ability to lock up the mirror before the shot is taken. This eliminates the vibration but blacks out the viewfinder. The SLR user cannot see anything outside the taking frame through the viewfinder, while with most rangefinder systems, this can be done. This helps in certain kinds of photography. Only higher-end SLRs show the full frame; typical coverage is 90%. Print labs generally crop an equivalent area, so it is less of a problem than it might otherwise be.

Format

SLR cameras have been produced for most film formats as well as digital formats. Most film SLRs use the 35 mm format, as this offers a good compromise between image quality, size, and cost. Medium format SLRs give a higher quality image when this is required. Digital SLRs (DSLRs) appeared on the market in the late 1990s and as of 2005 are used by many professional photographers as well as amateur enthusiasts. Early SLRs were built for large format photography, but this has largely died out. A small number of SLRs were built for the Advanced Photo System but this did not prove popular. SLRs were even built for film formats as small as 110, e.g. the Pentax Auto 110.

Common features

Other features found on many SLR cameras include through-the-lens (TTL) metering and sophisticated flash control. Many models on the market today actually measure the light that bounces off the film, and close the shutter when the picture has had enough exposure. Likewise, they can send out several short bursts of flash, determine the amount that comes back from the scene, then send out just the right amount of energy for a perfectly exposed photograph. Sophisticated cameras can even make it easy for the photographer to balance flash and available light for the desired look. While these capabilities are hardly unique to the SLR, manufacturers included them early on in the top models, whereas the best rangefinder cameras adopted such features later.

History

Large format SLR cameras were first built in the early years of the 20th century but were not very popular. Although the Soviet GOMZ sport (1935) was the first 35 mm SLR, it was the Ihagee Kine-Exakta (1936) that was truly influential. Further Exakta models, all with waist-level finders, were produced up to and during World War II. Meanwhile, Zeiss developed the eye-level viewfinder and pentaprism in prototype form, but the war intervened; in 1949 it saw production as the Contax S. It was the Japanese who developed the SLR further; the Asahi Optical Corporation was a pioneer in this, with 1952's Asahiflex. The Asahiflex IIB (1954) had the first auto-return mirror, while 1957's Asahi Pentax brought a fixed pentaprism, the right-hand thumb wind lever, and the overall control scheme of most manual-wind SLRs for the next 25 years or more. Modern-day market leaders Canon and Nikon introduced their first SLRs in 1959 (the Canonflex and F, respectively). The Nikon F was the camera that switched professional photographers to the 35 mm SLR. It was highly modular and versatile, and started the F series that continues to the present day. Through-the-lens (TTL) light metering came to the SLR in the early 1960s, with 1962's Topcon RE Sup