Camera Obscura

A camera obscura (; ) is a darkened room with a small hole or lens at one side through which an image is projected onto a wall or table opposite the hole.

''Camera obscura'' can also refer to analogous constructions such as a box or tent in which an exterior image is projected inside. Camera obscuras with a lens in the opening have been used since the second half of the 16th century and became popular as aids for drawing and painting. The concept was developed further into the photographic camera in the first half of the 19th century, when camera obscura boxes were used to expose light-sensitive materials to the projected image.

The camera obscura was used to study eclipses without the risk of damaging the eyes by looking directly into the sun. As a drawing aid, it allowed tracing the projected image to produce a highly accurate representation, and was especially appreciated as an easy way to achieve proper graphical perspective.

Before the term ''camera obscura'' was first used in 1604, other terms were used to refer to the devices: ''cubiculum obscurum'', ''cubiculum tenebricosum'', ''conclave obscurum'', and ''locus obscurus''.

A camera obscura without a lens but with a very small hole is sometimes referred to as a pinhole camera, although this more often refers to simple (homemade) lensless cameras where photographic film or photographic paper is used.

Physical explanation

Rays of light travel in straight lines and change when they are reflected and partly absorbed by an object, retaining information about the color and brightness of the surface of that object. Lighted objects reflect rays of light in all directions. A small enough opening in a barrier admits only the rays that travel directly from different points in the scene on the other side, and these rays form an image of that scene where they reach a surface opposite from the opening.

The human eye (and those of animals such as birds, fish, reptiles etc.) works much like a camera obscura with an opening ( pupil), a convex lens, and a surface where the image is formed (retina). Some cameras obscura use a concave mirror for a focusing effect similar to a convex lens.

Technology

A camera obscura consists of a box, tent, or room with a small hole in one side or the top. Light from an external scene passes through the hole and strikes a surface inside, where the scene is reproduced, inverted (upside-down) and reversed (left to right), but with color and perspective preserved.

To produce a reasonably clear projected image, the aperture is typically smaller than 1/100th the distance to the screen.
As the pinhole is made smaller, the image gets sharper, but dimmer. With a too small pinhole, however, the sharpness worsens, due to diffraction. Optimum sharpness is attained with an aperture diameter approximately equal to the geometric mean of the wavelength of light and the distance to the screen.

In practice, camera obscuras use a lens rather than a pinhole because it allows a larger aperture, giving a usable brightness while maintaining focus.

If the image is caught on a translucent screen, it can be viewed from the back so that it is no longer reversed (but still upside-down). Using mirrors, it is possible to project a right-side-up image. The projection can also be displayed on a horizontal surface (e.g., a table). The 18th-century overhead version in tents used mirrors inside a kind of periscope on the top of the tent.

The box-type camera obscura often has an angled mirror projecting an upright image onto tracing paper placed on its glass top. Although the image is viewed from the back, it is reversed by the mirror.

History

Prehistory to 500 BC: Possible inspiration for prehistoric art and possible use in religious ceremonies, gnomons

There are theories that occurrences of camera obscura effects (through tiny holes in tents or in screens of animal hide) inspired paleolithic cave paintings. Distortions in the shapes of animals in many paleolithic cave artworks might be inspired by distortions seen when the surface on which an image was projected was not straight or not in the right angle.
It is also suggested that camera obscura projections could have played a role in Neolithic structures.

Perforated gnomons projecting a pinhole image of the sun were described in the Chinese ''Zhoubi Suanjing'' writings (1046 BC–256 BC with material added until circa 220 AD). The location of the bright circle can be measured to tell the time of day and year. In Arab and European cultures its invention was much later attributed to Egyptian astronomer and mathematician Ibn Yunus around 1000 AD.

500 BC to 500 AD: Earliest written observations

One of the earliest known written records of a pinhole camera for camera obscura effect is found in the Chinese text called '' Mozi'', dated to the 4th century BC, traditionally ascribed to and named for Mozi (circa 470 BC-circa 391 BC), a Chinese philosopher and the founder of Mohist School of Logic. These writings explain how the image in a "collecting-point" or "treasure house"In the ''Mozi'' passage, a camera obscura is described as a "collecting-point" or "treasure house" ( 庫); the 18th-century scholar Bi Yuan () suggested this was a misprint for "screen" ( 㢓). is inverted by an intersecting point (pinhole) that collects the (rays of) light. Light coming from the foot of an illuminated person were partly hidden below (i.e., strike below the pinhole) and partly formed the top of the image. Rays from the head were partly hidden above (i.e., strike above the pinhole) and partly formed the lower part of the image.

Another early account is provided by Greek philosopher Aristotle (384–322 BC), or possibly a follower of his ideas. Similar to the later 11th-century Arab scientist Alhazen, Aristotle is also thought to have used camera obscura for observing solar eclipses. Camera obscura is touched upon as a subject in Aristotle's work '' Problems – Book XV'', asking: and further on:

Many philosophers and scientists of the Western world pondered this question before it was accepted that the circular and crescent-shapes described in the "problem" were pinhole image projections of the sun. Although a projected image has the shape of the aperture when the light source, aperture and projection plane are close together, the projected image has the shape of the light source when they are farther apart.

In his book ''Optics'' (circa 300 BC, surviving in later manuscripts from around 1000 AD), Euclid proposed mathematical descriptions of vision with "lines drawn directly from the eye pass through a space of great extent" and "the form of the space included in our vision is a cone, with its apex in the eye and its base at the limits of our vision." Later versions of the text, like Ignazio Danti's 1573 annotated translation, would add a description of the camera obscura principle to demonstrate Euclid's ideas.

500 to 1000: Earliest experiments, study of light

In the 6th century, the Byzantine-Greek mathematician and architect Anthemius of Tralles (most famous as a co-architect of the Hagia Sophia) experimented with effects related to the camera obscura.G. Huxley (1959) ''Anthemius of Tralles: a study of later Greek Geometry'' pp. 6–8, pp.44–46 as cited in , p.205 Anthemius had a sophisticated understanding of the involved optics, as demonstrated by a light-ray diagram he constructed in 555 AD.

In the 10th century Yu Chao-Lung supposedly projected images of pagoda models through a small hole onto a screen to study directions and divergence of rays of light.

1000 to 1400: Optical and astronomical tool, entertainment

Arab physicist Ibn al-Haytham (known in the West by the Latinised Alhazen) (965–1040) extensively studied the camera obscura phenomenon in the early 11th century.

In his treatise "On the shape of the eclipse" he provided the first experimental and mathematical analysis of the phenomenon.
He must have understood the relationship between the focal point and the pinhole.

In his '' Book of Optics'' (circa 1027), Ibn al-Haytham explained that rays of light travel in straight lines and are distinguished by the body that reflected the rays, writing:
He described a "dark chamber", and experimented with light passing through small pinholes, using three adjacent candles and seeing the effects on the wall after placing a cutout between the candles and the wall.

Ibn al-Haytham also analyzed the rays of sunlight and concluded that they made a conic shape where they met at the hole, forming another conic shape reverse to the first one from the hole to the opposite wall in the dark room. Latin translations of his writings on optics were very influential in Europe from about 1200 onward. Among those he inspired were Witelo, John Peckham, Roger Bacon, Leonardo da Vinci, René Descartes and Johannes Kepler.

In his 1088 book, '' Dream Pool Essays'', the Song Dynasty Chinese scientist Shen Kuo (1031–1095) compared the focal point of a concave burning-mirror and the "collecting" hole of camera obscura phenomena to an oar in a rowlock to explain how the images were inverted:

Shen Kuo also responded to a statement of Duan Chengshi in '' Miscellaneous Morsels from Youyang'' written in about 840 that the inverted image of a Chinese pagoda tower beside a seashore, was inverted because it was reflected by the sea: "This is nonsense. It is a normal principle that the image is inverted after passing through the small hole."

English statesman and scholastic philosopher Robert Grosseteste (c. 1175 – 9 October 1253) was one of the earliest Europeans who commented on the camera obscura.

English philosopher and Franciscan friar Roger Bacon (c. 1219/20 – c. 1292) falsely stated in his ''De Multiplicatione Specerium'' (1267) that an image projected through a square aperture was round because light would travel in spherical waves and therefore assumed its natural shape after passing through a hole. He is also credited with a manuscript that advised to study solar eclipses safely by observing the rays passing through some round hole and studying the spot of light they form on a surface.

A picture of a three-tiered camera obscura (see illustration) has been attributed to Bacon, but the source for this attribution is not given. A very similar picture is found in Athanasius Kircher's '' Ars Magna Lucis et Umbrae'' (1646).

Polish friar, theologian, physicist, mathematician and natural philosopher Erazmus Ciołek Witelo (also known as Vitello Thuringopolonis and by many different spellings of the name "Witelo") wrote about the camera obscura in his very influential treatise ''Perspectiva'' (circa 1270–1278), which was largely based on Ibn al-Haytham's work.

English archbishop and scholar John Peckham (circa 1230 – 1292) wrote about the camera obscura in his ''Tractatus de Perspectiva'' (circa 1269–1277) and ''Perspectiva communis'' (circa 1277–79), falsely arguing that light gradually forms the circular shape after passing through the aperture. His writings were influenced by Roger Bacon.

At the end of the 13th century, Arnaldus de Villa Nova is credited with using a camera obscura to project live performances for entertainment.

French astronomer Guillaume de Saint-Cloud suggested in his 1292 work ''Almanach Planetarum'' that the eccentricity of the sun could be determined with the camera obscura from the inverse proportion between the distances and the apparent solar diameters at apogee and perigee.

Kamāl al-Dīn al-Fārisī (1267–1319) described in his 1309 work ''Kitab Tanqih al-Manazir'' (''The Revision of the Optics'') how he experimented with a glass sphere filled with water in a camera obscura with a controlled aperture and found that the colors of the rainbow are phenomena of the decomposition of light.

French Jewish philosopher, mathematician, physicist and astronomer/astrologer Levi ben Gershon (1288–1344) (also known as Gersonides or Leo de Balneolis) made several astronomical observations using a camera obscura with a Jacob's staff, describing methods to measure the angular diameters of the sun, the moon and the bright planets Venus and Jupiter. He determined the eccentricity of the sun based on his observations of the summer and winter solstices in 1334. Levi also noted how the size of the aperture determined the size of the projected image. He wrote about his findings in Hebrew in his treatise ''Sefer Milhamot Ha-Shem'' (''The Wars of the Lord'') Book V Chapters 5 and 9.

1450 to 1600: Depiction, lenses, drawing aid, mirrors

Italian polymath Leonardo da Vinci (1452–1519), familiar with the work of Alhazen in Latin translation, and after an extensive study of optics and human vision, wrote the oldest known clear description of the camera obscura in mirror writing in a notebook in 1502, later published in the collection '' Codex Atlanticus'' (translated from Latin):

These descriptions, however, would remain unknown until Venturi deciphered and published them in 1797.

Da Vinci was clearly very interested in the camera obscura: over the years he drew circa 270 diagrams of the camera obscura in his notebooks . He systematically experimented with various shapes and sizes of apertures and with multiple apertures (1, 2, 3, 4, 8, 16, 24, 28 and 32). He compared the working of the eye to that of the camera obscura and seemed especially interested in its capability of demonstrating basic principles of optics: the inversion of images through the pinhole or pupil, the non-interference of images and the fact that images are "all in all and all in every part".

The oldest known published drawing of a camera obscura is found in Dutch physician, mathematician and instrument maker Gemma Frisius’ 1545 book ''De Radio Astronomica et Geometrica'', in which he described and illustrated how he used the camera obscura to study the solar eclipse of 24 January 1544

Italian polymath Gerolamo Cardano described using a glass disc – probably a biconvex lens – in a camera obscura in his 1550 book ''De subtilitate, vol. I, Libri IV''. He suggested to use it to view "what takes place in the street when the sun shines" and advised to use a very white sheet of paper as a projection screen so the colours wouldn't be dull.

Sicilian mathematician and astronomer Francesco Maurolico (1494–1575) answered Aristotle's problem how sunlight that shines through rectangular holes can form round spots of light or crescent-shaped spots during an eclipse in his treatise ''Photismi de lumine et umbra'' (1521–1554). However this wasn't published before 1611, after Johannes Kepler had published similar findings of his own.

Italian polymath Giambattista della Porta described the camera obscura, which he called "obscurum cubiculum", in the 1558 first edition of his book series '' Magia Naturalis''. He suggested to use a convex lens to project the image onto paper and to use this as a drawing aid. Della Porta compared the human eye to the camera obscura: "For the image is let into the eye through the eyeball just as here through the window". The popularity of Della Porta's books helped spread knowledge of the camera obscura.

In his 1567 work ''La Pratica della Perspettiva'' Venetian nobleman Daniele Barbaro (1513-1570) described using a camera obscura with a biconvex lens as a drawing aid and points out that the picture is more vivid if the lens is covered as much as to leave a circumference in the middle.

In his influential and meticulously annotated Latin edition of the works of Ibn al-Haytham and Witelo, (1572), German mathematician Friedrich Risner proposed a portable camera obscura drawing aid; a lightweight wooden hut with lenses in each of its four walls that would project images of the surroundings on a paper cube in the middle. The construction could be carried on two wooden poles. A very similar setup was illustrated in 1645 in Athanasius Kircher's influential book ''Ars Magna Lucis Et Umbrae''.

Around 1575 Italian Dominican priest, mathematician, astronomer, and cosmographer Ignazio Danti designed a camera obscura gnomon and a meridian line for the Basilica of Santa Maria Novella, Florence and he later had a massive gnomon built in the San Petronio Basilica in Bologna. The gnomon was used to study the movements of the sun during the year and helped in determining the new Gregorian calendar for which Danti took place in the commission appointed by Pope Gregorius XIII and instituted in 1582.

In his 1585 book ''Diversarum Speculationum Mathematicarum'' Venetian mathematician Giambattista Benedetti proposed to use a mirror in a 45-degree angle to project the image upright. This leaves the image reversed, but would become common practice in later camera obscura boxes.

Giambattista della Porta added a "lenticular crystal" or biconvex lens to the camera obscura description in the 1589 second edition of ''Magia Naturalis''. He also described use of the camera obscura to project hunting scenes, banquets, battles, plays, or anything desired on white sheets. Trees, forests, rivers, mountains "that are really so, or made by Art, of Wood, or some other matter" could be arranged on a plain in the sunshine on the other side of the camera obscura wall. Little children and animals (for instance handmade deer, wild boars, rhinos, elephants, and lions) could perform in this set. "Then, by degrees, they must appear, as coming out of their dens, upon the Plain: The Hunter he must come with his hunting Pole, Nets, Arrows, and other necessaries, that may represent hunting: Let there be Horns, Cornets, Trumpets sounded: those that are in the Chamber shall see Trees, Animals, Hunters Faces, and all the rest so plainly, that they cannot tell whether they be true or delusions: Swords drawn will glister in at the hole, that they will make people almost afraid."
Della Porta claimed to have shown such spectacles often to his friends. They admired it very much and could hardly be convinced by Della Porta's explanations that what they had seen was really an optical trick.

1600 to 1650: Name coined, camera obscura telescopy, portable drawing aid in tents and boxes

The earliest use of the term "camera obscura" is found in the 1604 book ''Ad Vitellionem Paralipomena'' by German mathematician, astronomer, and astrologer Johannes Kepler. Kepler discovered the working of the camera obscura by recreating its principle with a book replacing a shining body and sending threads from its edges through a many-cornered aperture in a table onto the floor where the threads recreated the shape of the book. He also realized that images are "painted" inverted and reversed on the retina of the eye and figured that this is somehow corrected by the brain.
In 1607, Kepler studied the sun in his camera obscura and noticed a sunspot, but he thought it was Mercury transiting the sun.
In his 1611 book ''Dioptrice'', Kepler described how the projected image of the camera obscura can be improved and reverted with a lens. It is believed he later used a telescope with three lenses to revert the image in the camera obscura.

In 1611, Frisian/German astronomers David and Johannes Fabricius (father and son) studied sunspots with a camera obscura, after realizing looking at the sun directly with the telescope could damage their eyes. They are thought to have combined the telescope and the camera obscura into camera obscura telescopy.

In 1612, Italian mathematician Benedetto Castelli wrote to his mentor, the Italian astronomer, physicist, engineer, philosopher, and mathematician Galileo Galilei about projecting images of the sun through a telescope (invented in 1608) to study the recently discovered sunspots. Galilei wrote about Castelli's technique to the German Jesuit priest, physicist, and astronomer Christoph Scheiner.

From 1612 to at least 1630, Christoph Scheiner would keep on studying sunspots and constructing new telescopic solar-projection systems. He called these "Heliotropii Telioscopici", later contracted to helioscope. For his helioscope studies, Scheiner built a box around the viewing/projecting end of the telescope, which can be seen as the oldest known version of a box-type camera obscura. Scheiner also made a portable camera obscura.

In his 1613 book ''Opticorum Libri Sex'' Belgian Jesuit mathematician, physicist, and architect François d'Aguilon described how some charlatans cheated people out of their money by claiming they knew necromancy and would raise the specters of the devil from hell to show them to the audience inside a dark room. The image of an assistant with a devil's mask was projected through a lens into the dark room, scaring the uneducated spectators.

By 1620 Kepler use