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
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
Image
capture
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
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 standardization for the more popular cameras. The
introduction of roll film
drove the standardization 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 adapter:
sometimes called a step-ring, adapts the lens to other size filters
•
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.
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
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.
The view camera is a type of camera first developed in
the era of the daguerreotype[1] (1840s-'50s) and still in use today, though with many refinements. It
comprises a flexible bellows which forms a light-tight seal between two adjustable standards, one of which holds a lens, and the other a viewfinder or a photographic
filmholder.[2]
The bellows is a flexible, accordion-pleated box, which encloses the
space between the lens and film, and has the ability to flex to accommodate the
movements of the standards.[3]
The front standard is a board at the front of the camera
which holds the lens and, usually, a shutter.
At the other end of the bellows, the rear
standard is a frame which
holds a ground glass, used for
focusing and composing the image before exposure, which is replaced by a holder
containing the light-sensitive film, plate, or image sensor for exposure. The front and rear standards can move in various ways relative to each other, unlike most other types of
camera, giving control over focus, depth of field and perspective.
Medium-format camera
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.
Medium format has traditionally
referred to a film
format in still photography and the related
cameras and equipment that use that film. Generally, the term applies to film
and digital cameras that record images on media larger than 24 by 36 mm (full-frame) (used in 35
mm photography), but smaller than 4 by 5 inches (which is
considered to be large-format photography).
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.
A folding
camera is a camera that can be folded to
a compact and rugged package when not in use. The camera objective is sometimes attached to a pantograph-like mechanism, in which the lid usually is a component. The
objective extends to give correctfocus when unfolded. A cloth
or leather bellows keeps the light out. When folded,
the camera has an excellent physical size to film size ratio. This feature was
very appealing when the only film formats available were large or medium format films.
The use of folding cameras began to decline after WWII
with the development of the 35mm
film format, which allowed the construction of small-sized cameras
without use of a bellows. However, some 35 mm cameras were also of the
folding type, such as the original Kodak Retina.
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.
The box
camera is mechanically simple,
the most common form is a cardboard or plastic box with a lens in one end and film at the other. The
lenses are often single element designs meniscus fixed
focus lens, or in better quality box cameras a doublet lens with
minimal (if any) possible adjustments to the aperture or shutter
speeds. Because of the inability to adjust focus, the small
lens aperture and the low sensitivity of the sensitive materials available,
these cameras work best in brightly lit daylit scenes when the subject is
within the hyperfocal distance for the lens and of subjects that
move little during the exposure -- snapshots. During the box cameras heyday, box cameras with photographic flash, shutter and aperture adjustment
were introduced, allowing indoor photos.
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.
A rangefinder
camera is a camera fitted
with a rangefinder: a range-finding focusing mechanism allowing the
photographer to measure the subject distance and take photographs that are in
sharp focus. Most varieties of rangefinder show two images of the same subject,
one of which moves when a calibrated wheel is turned; when the two images
coincide and fuse into one, the distance can be read off the wheel. Older,
non-coupled rangefinder cameras display the focusing distance and require the
photographer to transfer the value to the lens focus ring; cameras without
built-in rangefinders could have an external rangefinder fitted into the
accessory shoe. Earlier cameras of this type had separate viewfinder and rangefinder
windows; later the rangefinder was incorporated into the viewfinder. More
modern designs have rangefinders coupled to the focusing mechanism, so that the
lens is focused correctly when the rangefinder images fuse; compare with the focusing
screen in non-autofocus SLRs.
Single-lens
reflex
A single-lens
reflex (SLR) camera is a camera that typically uses a
mirror and prism system (hence "reflex", from the mirror's
reflection) that permits the photographer to view through the lens and see
exactly what will be captured, contrary toviewfinder cameras where the
image could be significantly different from what will be captured.
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
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
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.
With
a film camera, the light entering through the lens strikes the film. Developing
the film makes it possible to see the photograph that was taken.
With
a digital camera, the light entering through the lens strikes an image sensor.
The signal output by the image sensor is processed within the camera to create
image data, which is stored on the memory card. The image can be simultaneously
viewed on the picture display.
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.
USES OF PHOTOGRAPHIC CAMERA
It’s so easy now to take photographs of friends and family. With no need for film, a digital camera can be ready at any time, as long as the batteries are good. This is a great way to keep a record of your children–their growth, their birthdays, the important events in their lives.
Create insurance records
Digital cameras are an excellent way to keep a visual inventory for insurance purposes. While people have used camcorders to create a visual reference of collections and important physical assets, your digital camera will enable you to create not only overall views of objects, but detailed views as well.
Create Graphics for Web sites
Because digital photos are electronic, you can use your digital camera to create your own photos and graphics for your Web site, if you have one.
Create Virtual Reality Tours
Digital cameras are also good for creating virtual reality tours of you’re your home or business to present on the Web or to clients via a laptap computer.
Make Your Own Photo Business Cards
One of the hottest tools available to business people today is photo business cards. You can take your own photo using the self-timer on your digital camera and then place the photo into the design of your business card in your word processor or graphics program.
Produce Your Own Clip Art
Isn’t it frustrating to search through thousands of clip art images and not find the images you need? Now with your digital camera, you can produce your own clip art images, either taking regular photographs or close-ups.
Textures and Objects for Presentations
Digital cameras are great for recording textures for Web sites and presentations. You can also shoot exactly the objects you need, such as your business’ products, to use in Powerpoint presentations on our laptop.
Create Digital Photographic Art
Using a combination of your digital camera and more sophisticated photo editing software such as Adobe Photoshop, you can get creative and produce your own artistic creations–photo montages, blends, screen savers and wallpapers.
Record a Event or Meeting
What better way is there than to use a simple digital camera to record an historic event or an important meeting. Taking photos of the moving of an historic building or taking shots of unique booths at a trade show–both are easy with your digital camera.
ADVANTAGES
1 Established technology
2 Simple cabling standard that uses a
single BNC cable to connect the camera to the framegrabber.
3 Inexpensive, especially compared to
parallel standard and camera link digital cameras.
4 Standard resolution of 640 x 480
pixels at a speed 30 frames per second is sufficiend for most common
applications.
5 High speed, high pixel depth and
large image sizes.
6 Easy to configure camera options and
other functionality.
7 Does not require national instruments
hardware.
8 Supports a variety of frame rates and
image sizes.
9 Does not require camera files.
10 Lower cost.
11 wide selection.
DIS ADVANTAGES
1 No physical or protocol standards for
interfacing with framegrabbers.
2 Require custom cables and connectors.
3 Higher cost compared to analog, IEEE
1394, and Gigabit Ethernet standards.
4 Fewer products currently available.
5 Less triggering supports.
6 Depend on third party driver.
7 Difficult to synchronize with other
devices.
ACTIONS TO BE DONE WHEN YOU ARE USING A
PHOTOGRAPHIC CAMERA
Distractions - Avoid them!
Cropping - Do this with the camera first. Capture the most important part of the picture - the part that makes the story. Your pictures need to have a variety of types of croppings.
Perspective - Try to get interesting perspective that other photographers have not tried, or that you have not often seen. Bend your knees, and tippy-toe whenever necessary. Standing on a bench, chair, ladder, etc. can be an excellent helper.
Lighting - Use natural lighting whenever you can. You want to create a mood with your lighting. Watch where you have shadows. Any indoor picture may need a flash.
Action - Place yourself close to the action. Try to get people in action. Capture their daily activities. Sprts scenes lend themselves to fast action. When photographing sports, try to get as many faces as you can.
Contrast - Try to get your blacks as black as possible and your whites as white as possible. Contrast small shapes with large shapes.
Creativity - Create a new view of a common picture. See things in a way that you never noticed before. Crop your center of interest so that it is telling the whole story - showing faces, expressions, moods, movements, stances, situations, and experiences that we all share at one time or another. Find our likenesses and differences.
Consistency - Be as consistent as you can. At first this will be difficult, but it will slowly start to make an impression on you when you do certain things the same that give you good pictures. Follow that, so your pictures are the best possible.
Balance - Each picture has its own balance and should be pleasing to look at. It can be formally balalnced or informally balanced, but the basic principles of design apply here too. Try not to make something look like it is falling off the page, etc.
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