Camera

A camera is a device that records Latin for “dark chamber”), an early mechanism for projecting images. The modern camera evolved from the camera obscura.

Cameras may work with the photographic film.

A typical still camera takes one photo each time the user presses the film frames per second as long as the user holds down the shutter button, or until the shutter button is pressed a second time.

Contents

[edit] History

The forerunner to the photographic camera was the [8]

The actual name of camera obscura was applied by mathematician and astronomer [11]

The first camera obscura that was small enough for practical use as a portable drawing aid was built by Johann Zahn in 1685.[12] At that time there was no way to preserve the images produced by such cameras except by manually tracing them. However, it had long been known that various substances were bleached or darkened or otherwise changed by exposure to light. Seeing the magical miniature pictures that light temporarily “painted” on the screen of a small camera obscura inspired several experimenters to search for some way of automatically making highly detailed permanent copies of them by means of some such substance.

Early photographic cameras were usually in the form of a pair of nested boxes, the end of one carrying the lens and the end of the other carrying a removable ground glass focusing screen. By sliding them closer together or farther apart, objects at various distances could be brought to the sharpest focus as desired. After a satisfactory image had been focused on the screen, the lens was covered and the screen was replaced with the light-sensitive material. The lens was then uncovered and the exposure continued for the required time, which for early experimental materials could be several hours or even days. The first permanent photograph of a camera image was made in 1826 by Joseph Nicéphore Niépce using a sliding wooden box camera made by Charles and Vincent Chevalier in Paris.[13]

Similar cameras were used for exposing the silver-surfaced copper bellows for focusing became widespread, making the bulkier and less easily adjusted nested box design obsolete.

For many years, exposure times were long enough that the photographer simply removed the lens cap, counted off the number of seconds (or minutes) estimated to be required by the lighting conditions, then replaced the cap. As more sensitive photographic materials became available, cameras began to incorporate mechanical shutter mechanisms that allowed very short and accurately timed exposures to be made.

The electronic digital cameras, which largely supplanted film cameras around the start of the 21st century.

[edit] Mechanics

[edit] Image capture

19th century studio camera, with bellows for focusing

Traditional cameras capture light onto processing.

Cameras that capture many images in sequence are known as video camera is a category of movie camera that captures images electronically (either using analog or digital technology).

[edit] Lens

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 19th 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 Leitz.

Camera lenses are made in a wide range of focal lengths. They range from extreme wide angle, wide angle, standard, medium telephoto and telephoto. Each lens is best suited a certain type of photography. The extreme wide angle may be preferred for architecture because it has the capacity to capture a wide view of a building. The normal lens, because it often has a wide aperture, is often used for street and documentary photography. The telephoto lens is useful for sports, and wildlife but it is more susceptible to camera shake.[14]

[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.[15]

Some experimental cameras, for example the planar Fourier capture array (PFCA), do not require focusing to allow them to take pictures. In conventional digital photography, lenses or mirrors map all of the light originating from a single point of an in-focus object to a single point at the sensor plane. Each pixel thus relates an independent piece of information about the far-away scene. In contrast, a PFCA does not have a lens or mirror, but each pixel has an idiosyncratic pair of diffraction gratings above it, allowing each pixel to likewise relate an independent piece of information (specifically, one component of the 2D Fourier transform) about the far-away scene. Together, complete scene information is captured and images can be reconstructed by computation.

Some cameras have post focusing. Post focusing means take the pictures first and then focusing later at the [17]

[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

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 Leaf 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. Disadvantages of such shutters are their inability to reliably produce very fast shutter speeds ( faster than 1/500th second or so) and the additional cost and weight of having to include a shutter mechanism for every lens.

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 (typically running horizontally) or consisting of a series of metal plates (typically moving vertically) just in front of the film plane. The focal-plane shutter is primarily associated with the single lens reflex type of cameras, since covering the film rather than blocking light passing through the lens allows the photographer to view through the lens at all times except during the exposure itself. Covering the film also facilitates removing the lens from a loaded camera (many SLRs have interchangeable lenses).

[edit] Complexities

Professional 120/220 roll film) use a hybrid solution, since such a large focal-plane shutter would be difficult to make and/or may run slowly. A manually inserted blade known as a dark slide allows the film to be covered when changing lenses or film backs. A blind inside the camera covers the film prior to and after the exposure (but is not designed to be able to give accurately controlled exposure times) and a leaf shutter that is normally open is installed in the lens. To take a picture, the leaf shutter closes, the blind opens, the leaf shutter opens then closes again, and finally the blind closes and the leaf shutter re-opens (the last step may only occur when the shutter is re-cocked).

Using a focal-plane shutter, exposing the whole film plane can take much longer than the exposure time. The exposure time does not depend on the time taken to make the exposure over all, only on the difference between the time a specific point on the film is uncovered and then covered up again. 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. In fact in practice the curtains do not run at a constant speed as they would in an ideal design, obtaining an even exposure time depends mainly on being able to make the two curtains accelerate in a similar manner.

When photographing rapidly moving objects, the use of a focal-plane shutter can produce some unexpected effects, since the film closest to the start position of the curtains is exposed earlier than the film closest to the end position. Typically this can result in a moving object leaving a slanting image. The direction of the slant depends on the direction the shutter curtains run in (noting also that as in all cameras the image is inverted and reversed by the lens, i.e. “top-left” is at the bottom right of the sensor as seen by a photographer behind the camera).

Focal-plane shutters are also difficult to synchronise with electronic flash and it is often only possible to use flash at shutter speeds where the curtain that opens to reveal the film completes its run and the film is fully uncovered, before the second curtain starts to travel and cover it up again. Typically 35mm film SLRs could sync flash at only up to 1/60th second if the camera has horizontal run cloth curtains, and 1/125th if using a vertical run metal shutter.

[edit] Film formats

French 12×12″ collodion camera (ca. 1878) next to a 35 mm SLR Nikon F (ca. 1970)

A wide range of film and plate formats has 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 Leica Camera range.

For cine cameras, film 35 mm wide and perforated with film frames, was introduced in 1965.

[edit] Camera accessories

Accessories for cameras are mainly for care, protection, special effects and functions.

  • Lens hood: used on the end of a lens to block the sun or other light source to prevent glare and lens flare.
  • Lens cover: covers and protects the lens during storage
  • Lens adapter: sometimes called a step-ring, adapts the lens to other size filters
  • Lens extension tubes allow close focus in macro photography
  • Flash equipment: including soft box, trigger and cord
  • Care and protection: including camera case and cover, maintenance tools, and screen protector
  • Large format cameras use special equipment which includes magnifier loupe, view finder, angle finder, focusing rail /truck.
  • Battery and charger[19]

[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. To make the exposure, the dark slide was carefully slid out and the shutter opened and then closed and the dark slide replaced. Glass plates were later replaced by sheet film in a dark slide for sheet film; adaptor sleeves were made to allow sheet film to be used in plate holders. In addition to the ground glass, a simple optical viewfinder was often fitted.[20]

Cameras which take single exposures on sheet film and are functionally identical to plate cameras are still used for static, high-image-quality work; see Large-format camera, below.

[edit] Large-format camera

The large-format camera, taking ground-glass screen which is replaced by the film to make the exposure; they are suitable for static subjects only, and are slow to use.

[edit] Medium-format camera

Medium-format cameras have a film size between the large-format cameras and smaller 35mm cameras. Typically these systems use 120 or 220 rollfilm. The most common image sizes are 6×4.5 cm, 6×6 cm and 6×7 cm; the older 6×9 cm is rarely used. The designs of this kind of camera show greater variation than their larger brethren, ranging from monorail systems through the classic 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. Folding rollfilm cameras were preceded by folding plate cameras, more compact than other designs.[20]

[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 focusing 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 reduce the impact of deficiencies in the lens.

[edit] Rangefinder camera

As camera and lens technology developed and wide aperture lenses became more common, interchangeable lenses, each lens requiring its own range- and viewfinder linkages.

Rangefinder cameras were produced in half- and full-frame 35 mm and rollfim (medium format).

[edit] Single-lens reflex

In the single-lens reflex camera the photographer sees the scene through the camera lens. This avoids the problem 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 6×9, 6×6 and 6×4.5 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 [22]

[edit] Twin-lens reflex

Twin-lens reflex cameras used a pair of nearly identical lenses, one to form the image and one as a viewfinder. The lenses 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 allow 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. Most TLRs used 120 or 220 film; some used the smaller 127 film.

[edit] Subminiature camera

Cameras taking film significantly smaller than 35 mm were made. Subminiature cameras were first produced in the nineteenth century. The expensive 8×11 mm espionage (the Minox company later also produced larger cameras). Later inexpensive subminiatures were made for general use, some using rewound 16 mm cine film. Image quality with these small film sizes was limited.

[edit] Ciné camera

A ciné camera or movie camera 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.

Ciné-Kodak Special II – 16mm movie camera (ca. 1948)

The frames are later played back in a ciné projector at a specific speed, called the “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 very small and light for single-handed operation. In the last quarter of the 20th century Professional video cameras did the same for professional users around the start of the 20th century.

[edit] Image gallery

[edit] See also

[edit] Types

[edit] Brands

[edit] Other

[edit] References

  1. 0-262-52259-4. “The camera obscura looms large in traditional historical accounts of photography’s invention.”
  2. ^ Hirsch, pp. 3-4
  3. ^ Gustavson, p. 4
  4. ^ Johnson, Rice, and Williams, p. 36
  5. ^ c Hirsch, p. 4
  6. ^ Gernsheim, pp. 3-4
  7. ^ Frizot, p. 18
  8. ^ Gernsheim, p. 3
  9. 0-415-97665-0.
  10. 0-7614-2596-9.
  11. ^ Explanatory Notes (section) of David Constantine’s 1994 translation of Goethe’s Elective Affinities, Oxford University Press.
  12. ^ Gersheim, p. 5
  13. ^ Gersheim, pp. 9-11
  14. ^ “Understanding Camera Lenses”. Cambridgeincolour.com. http://www.cambridgeincolour.com/tutorials/camera-lenses.htm. Retrieved 2010-07-29.
  15. ^ Auto focus – How Stuff Works
  16. ^ “New cameras use thousands of tiny lenses to let you focus after shooting”. June 22, 2011. http://www.tecca.com/news/2011/06/22/plenoptics-raytrix-lytro/.
  17. ^ “Lytro camera lets you focus after shooting, now available for pre-order”. http://news.yahoo.com/blogs/technology-blog/lytro-camera-lets-focus-shooting-now-available-pre-003019940.html. Retrieved October 20, 2011.
  18. ^ Accessories to Photography
  19. ^ Oxford Dictionary
  20. ^ Goerz Taro-Tenax, a folding 9×12 cm plate camera with some lens movements and optical viewfinder
  21. ^ Canon Pellix QL / FT QL Cameras (retrieved 19 April 2009)
  22. ^ The Periflex series (retrieved 19 April 2009)

[edit] Bibliography

  • Frizot, Michel. “Light machines: On the threshold of invention”. In Michel Frizot. A New History of Photography. Koln, Germany: Konemann. ISBN 3-8290-1328-0.
  • Gernsheim, Helmut (1986). A Concise History of Photography (3 ed.). Mineola, New York: Dover Publications, Inc. ISBN 0-486-25128-4.
  • Gustavson, Todd (2009). Camera: a history of photography from daguerreotype to digital. New York, New York: Sterling Publishing Co., Inc. ISBN 978-1-4027-5656-6.
  • Hirsch, Robert (2000). Seizing the Light: A History of Photography. New York, New York: McGraw-Hill Companies, Inc. ISBN 0-697-14361-9.
  • Johnson, William S.; Rice, Mark; Williams, Carla (2005). Therese Mulligan and David Wooters. ed. A History of Photography. Los Angeles, California: Taschen America. ISBN 978-3-8228-4777-0.

[edit] External links



This article uses material from the Wikipedia article Camera, which is released under the Creative Commons Attribution-Share-Alike License 3.0.