PHOTOGRAPHIC CAMERA



INTRODUCTION

A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the word camera obscura, an early mechanism for projecting images..
Cameras may work with the light of the visible spectrum or with other portions of the electromagnetic spectrum. A camera generally consists of an enclosed hollow with an opening (aperture) at one end for light to enter, and a recording or viewing surface for capturing the light at the other end. A majority of cameras have a lens positioned in front of the camera's opening to gather the incoming light and focus all or part of the image on the recording surface. The diameter of the aperture is often controlled by a diaphragm mechanism, but some cameras have a fixed-size aperture. Most 20th century cameras used photographic film as a recording surface, while the majority of new ones now use an electronic image sensor.
The still camera takes one photo each time the user presses the shutter button. A typical movie camera continuously takes 24 film frames per second as long as the user holds down the shutter button, or until the shutter button is pressed a second time.


History of the camera




The forerunner to the photographic camera was the camera obscura.[1] In the fifth century B.C., the Chinese philosopher Mo Ti noted that a pinhole can form an inverted and focused image, when light passes through the hole and into a dark area. Mo Ti is the first recorded person to have exploited this phenomenon to trace the inverted image to create a picture.[3] Writing in the fourth century B.C., Aristotle also mentioned this principle.[4] He described observing a partial solar eclipse in 330 B.C. by seeing the image of the Sun projected through the small spaces between the leaves of a tree.[5] In the tenth century, the Arabic scholar Ibn al-Haytham (Alhazen) also wrote about observing a solar eclipse through a pinhole,[6] and he described how a sharper image could be produced by making the opening of the pinhole smaller. By the fifteenth century, artists and scientists were using this phenomenon to make observations. Originally, an observer had to enter an actual room, in a which a pinhole was made on one wall. On the opposite wall, the observer would view the inverted image of the outside.[7] The name camera obscura, Latin for "dark room", derives from this early implementation of the optical phenomenon.[8]
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]
The Dubroni of 1864 allowed the sensitizing and developing of the plates to be carried out inside the camera itself rather than in a separate darkroom. Other cameras were fitted with multiple lenses for photographing several small portraits on a single larger plate, useful when making cartes de visite. It was during the wet plate era that the use of 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 video camera tube was invented in the 1920s, starting a line of development that eventually resulted in digital cameras, which largely supplanted film cameras after the turn of the 21st century.

Mechanics



19th century studio camera, with bellows for focusing
Traditional cameras capture light onto photographic film or photographic plate. Video and digital cameras use an electronic image sensor, usually a charge coupled device (CCD) or a CMOS sensor to capture images which can be transferred or stored in a memory card or other storage inside the camera for later playback or processing.
Cameras that capture many images in sequence are known as movie cameras or as ciné cameras; 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 many modern cameras can quickly switch between still and motion recording modes. A video camera is a category of movie camera that captures images electronically (either using analogue or digital technology).

Lens
 Camera lens and Photographic lens design


The lens of a camera captures the light from the subject and brings it to a focus on the film or detector. The design and manufacture of the lens is critical to the quality of the photograph being taken. The technological revolution in camera design in the 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 microscopes. Pioneers included Zeiss and 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]

 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]

 
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.




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).

Flashes

An external flash can give you a stronger flash of light than the flash that is built into the camera. With the type that allows you to change the angle of the flash head, you can spread out and soften the light by bouncing it off the wall or ceiling.

 Complexities
Professional medium format SLR cameras (typically using 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 flash bulbs and 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.

 Film formats
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 roll film drove the standardisation process still further so that by the 1950s only a few standard roll films were in use. These included 120 film providing 8, 12 or 16 exposures, 220 film providing 16 or 24 exposures, 127 film providing 8 or 12 exposures (principally in Brownie cameras) and 35 mm film providing 12, 20 or 36 exposures – or up to 72 exposures in the half-frame format or in bulk cassettes for the Leica Camera range.
For cine cameras, film 35 mm wide and perforated with sprocket holes was established as the standard format in the 1890s. It is still used for nearly all film-based professional motion picture production. For amateur use, several smaller and therefore less expensive formats were introduced. 17.5 mm film, created by splitting 35 mm film, was one early amateur format, but 9.5 mm film, introduced in Europe in 1922, and 16 mm film, introduced in the US in 1923, soon became the standards for "home movies" in their respective hemispheres. In 1932, the even more economical 8 mm format was created by doubling the number of perforations in 16 mm film, then splitting it, usually after exposure and processing. The Super 8 format, still 8 mm wide but with smaller perforations to make room for substantially larger film frames, was introduced in 1965.
Film types
Today, plastic film comes in various sizes and speeds, in a colour or a black and white format, packaged as rolls or plates. The speed, given in ASA/ISO or DIN numbers, indicates how quickly the film reacts to the light. A new device, the Electronic Film System, fits into a 35mm camera and holds up to 30 digital images which can be transferred to a computer.

 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 in order 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 light diffuser, mount and stand, reflector, 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[18][19]


Camera designs


 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. In current designs the plate camera is best represented by the view camera.

Large-format camera
Main article: View camera
The large format camera is a direct successor of the early plate cameras and remain in use for high quality photography and for technical, architectural and industrial photography. There are three common types, the monorail camera, the field camera and the press camera. All use large format sheets of film, although there are backs for medium format 120-film available for most systems, and have an extensible bellows with the lens and shutter mounted on a lens plate at the front. These cameras have a wide range of movements allowing very close control of focus and perspective.

 Medium-format camera
Main article: Medium-format
Medium-format cameras have a film size somewhere in between the large format cameras and the smaller 35mm cameras. Typically these systems use 120- or 220-film. The most common sizes being 6x4.5 cm, 6x6 cm and 6x7 cm. The designs of this kind of camera show greater variation than their larger brethren, ranging from monorail systems through the classic Hasselblad model with separate backs, to smaller rangefinder cameras. There are even compact amateur cameras available in this format.

 Folding camera
Main article: 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.

 Box camera
Main article: 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.

 Rangefinder camera
Main article: Rangefinder camera
As camera and lens technology developed and wide aperture lenses became more common, range-finder cameras were introduced to make focussing more precise. The range finder has two separated viewfinder windows, one of which is linked to the focusing mechanisms and moved right or left as the focusing ring is turned. The two separate images are brought together on a ground glass viewing screen. When vertical lines in the object being photographed meet exactly in the combined image, the object is in focus. A normal composition viewfinder is also provided.

 Single-lens reflex
Main article: Single-lens reflex camera


Olympus E-420 Four Thirds entry-level DSLR with a 25mm pancake lens.

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 6x9, 6x6 and 6x4.5 respectively (all dimensions in cm). Notable manufacturers of large format SLR include Hasselblad, Mamiya, Bronica and Pentax. However the most common format of SLRs has been 35 mm and subsequently the migration to digital SLRs, using almost identical sized bodies and sometimes using the same lens systems.

Almost all SLR used a front surfaced mirror in the optical path to direct the light from the lens via a viewing screen and pentaprism to the eyepiece. At the time of exposure the mirror flipped up out of the light path before the shutter opened. Some early cameras experimented other methods of providing through the lens viewing including the use of a semi transparent pellicle as in the Canon Pellix[20] and others with a small periscope such as in the Corfield Periflex series.[21]




Twin-lens reflex
Main article: Twin-lens reflex camera
Twin-lens reflex cameras used a pair of nearly identical lenses, one to form the image and one as a viewfinder. The 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. Although most TLRs used 120 or 220 film some used 127 film.

Ciné camera
Main article: Movie 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. The frames are later played back in a ciné projector at a specific speed, called the "frame rate" (number of frames per second). While viewing, a person's eyes and brain merge the separate pictures to create the illusion of motion. The first ciné camera was built around 1888 and by 1890 several types were being manufactured. The standard film size for ciné cameras was quickly established as 35mm film and this remains in use to this day. Other professional standard formats include 70 mm film and 16mm film whilst amateurs film makers used 9.5 mm film, 8mm film or Standard 8 and Super 8 before the move into digital format.

The size and complexity of ciné cameras varies greatly depending on the uses required of the camera. Some professional equipment is very large and too heavy to be hand held whilst some amateur cameras were designed to be very small and light for single-handed operation. In the last quarter of the 20th century camcorders supplanted film motion cameras for amateurs. Professional video cameras did the same for professional users around the turn of the century.
Photographic Mechanism of Camera
With a digital camera, photographs can be viewed on the spot since the film development step required for film cameras is not necessary.


Working of Photographic Camera
The working of a camera is based on the fundamentals of reflection. As we know light travels through different media at different speeds. So the speed of light would vary when it travels in air than when it travels through a glass medium. When you focus on an object, light bounces of it and strikes the glass or plastic lens. This slows down the speed and of light and allows the rays to bend as they enter the lens. So as the light rays diverge from the source, the lens allow the rays to converge on a single point where the image can be formed. Commonly known as the film surface of a camera, this light sensitive material records the image. Later when processed with certain chemicals the image is visible.

Along with this basic structure a manual camera may also contain an aperture control, a diaphragm that regulates the amount of light that enters a lens and shutter just before the light sensor. The function of the shutter is to expose the light sensor to a consistent amount of light. So the amount of time the shutter is open determines the amount of light that reaches the film/light sensor surface. The shutter speed or rather the time that the shutters are left open is how photographers control picture quality and certain effects such as the picture of a moving object with the blurring.

A digital camera takes light and focuses it via the lens onto a sensor made out of silicon. It is made up of a grid of tiny photosites that are sensitive to light. Each photosite is usually called a pixel, a contraction of "picture element". There are millions of these individual pixels in the sensor of a DSLR camera.
Digital cameras sample light from our world, or outer space, spatially, tonally and by time. Spatial sampling means the angle of view that the camera sees is broken down into the rectangular grid of pixels. Tonal sampling means the continuously varying tones of brightness in nature are broken down into individual discrete steps of tone. If there are enough samples, both spatially and tonally, we perceive it as faithful representation of the original scene. Time sampling means we make an exposure of a given duration.
Each photosite on a CCD or CMOS chip is composed of a light-sensitive area made of crystal silicon in a photodiode which absorbs photons and releases electrons through the photoelectric effect. The electrons are stored in a well as an electrical charge that is accumulated over the length of the exposure. The charge that is generated is proportional to the number of photons that hit the sensor.
This electric charge is then transferred and converted to an analog voltage that is amplified and then sent to an Analog to Digital Converter where it is digitized (turned into a number)
CCD and CMOS sensors perform similarly in absorbing photons, generating electrons and storing them, but differ in how the charge is transferred and where it is converted to a voltage. Both end up with a digital output.
The entire digital image file is then a collection of numbers that represent the location and brightness values for each square in the array. These numbers are stored in a file that our computers can work with.
The entire photosite is not light sensitive. Only the photodiode is. The percentage of the photosite that is light sensitive is called the fill factor. For some sensors, such as CMOS chips, the fill factor may only be 30 to 40 percent of the entire photosite area. The rest of the area on a CMOS sensor is comprised of electronic circuitry, such as amplifiers and noise-reduction circuits.
Because the light-sensitive area is so small in comparison to the size of the photosite, the overall sensitivity of the chip is reduced. To increase the fill factor, manufacturers use micro-lenses to direct photons that would normally hit non-sensitive areas and otherwise go undetected, to the photodiode.
Electrons are generated as long as photons strike the sensor during the duration of the exposure or integration. They are stored in a potential well until the exposure is ended. The size of the well is called the full-well capacity and it determines how many electrons can be collected before it fills up and registers as full. In some sensors once a well fills up, the electrons can spill over into adjacent wells, causing blooming, which is visible as vertical spikes on bright stars. Some cameras have anti-blooming features that reduce or prevent this. Most DSLR cameras control blooming very well and it is not a problem for astrophotography.
The number of electrons that a well can accumulate also determines the sensor's dynamic range, the range of brightness from black to white where the camera can capture detail in both the faint and bright areas in the scene. Once noise is factored in, a sensor with a larger full-well capacity usually has a larger dynamic range. A sensor with lower noise helps improve the dynamic range and improves detail in weakly illuminated areas.

Functioning of Traditional, Digital, Video cameras


Traditional Cameras
A traditional camera functions by manipulating light much the same way a human eye does. When someone looks at an object, light essentially bounces off that object. The light goes into a person's eye, and a picture is sent to the retina. A camera functions the same way--light from an object goes in through the aperture. The aperture is a small hole located on or in front of the lens cover. It can get bigger or smaller depending on how much light you want to get in. The light hits the camera lens, which then allows a person to focus the image created from that light onto a piece of film located inside the camera body. When you "click," a button on a traditional camera, the image created from the light getting in, is essentially locked onto the film inside. You use a film advance lever to get a blank piece of film to lock another image onto it.

Digital Cameras
A digital camera functions much the same way a traditional camera does. It has all the essential parts, lens cover, lens and aperture. The inside of the camera has to function a little differently to generate in image, however. A digital camera actually makes an electronic recording of the image created by light entering into the camera body. A computer chip registers the information as a series of ones and zeros--just like on a regular PC computer, for example. A digital camera can translate electronic information into pixels. Pixels are simply collections of digital squares all scrambled around. You can think of pixels like pieces of a puzzle. How clear a picture might be depends on the resolution, which refers to the degree of detail that can be found in a digital image.

Video Cameras
Video cameras function as both a camera and recording device. A piece of videotape functions much like the film in the back of a camera--it just has more information encoded onto it, including sound. Digital camcorders do not have tape, but much like the digital camera, it translates information electronically. It takes information received from light and images, and changes it into pieces of data--those 1s and 0s and pixels that ultimately determine the level of resolution, or picture detail. Instead of recording audio separately from the light image, as was the case with older model video cameras, digital camcorders simultaneously marry both the image and sound electronically.