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Photography is the process of recording pictures by
means of capturing light on a light-sensitive medium, such as a film
or electronic sensor (in Digital Photography). Light patterns
reflected or emitted from objects expose a sensitive silver halide
based chemical or electronic medium during a timed exposure, usually
through a photographic lens in a device known as a camera that also
stores the resulting information chemically or electronically. The
camera or camera obscura is the image-forming device, and
photographic film or a silicon electronic image sensor is the sensing
medium. The respective recording medium can be the film itself, or a
digital electronic or magnetic memory. Photographers control the
camera and lens to "expose" the light recording material
(such as film) to the required amount of light to form a "latent
image" (on film) or "raw file" (in digital cameras)
which, after appropriate processing, is converted to a usable image.
Modern digital cameras replace film with an electronic image sensor
based on light-sensitive electronics such as charge-coupled device
(CCD) or complementary metal-oxide-semiconductor (CMOS) technology.
The resulting digital image is stored electronically, but can be
reproduced on paper or film.
A camera is a device used to capture images, either as
still photographs or as sequences of moving images (movies or
videos). The term comes from the Latin camera obscura for "dark
chamber" for an early mechanism of projecting images where an
entire room functioned as a real-time imaging system; the modern
camera evolved from the camera obscura.
In optics, an aperture is a hole or an opening through
which light is admitted. More specifically, the aperture of an
optical system is the opening that determines the cone angle of a
bundle of rays that come to a focus in the image plane. The aperture
determines how collimated the admitted rays are, which is of great
importance for the appearance at the image plane. If the admitted
rays also pass through a lens, highly collimated rays (narrow
aperture) will result in sharpness at the image plane, while
uncollimated rays (wide aperture) will result in sharpness for rays
with the right focal length only.
Exposure is the total amount of light allowed to fall
on the photographic medium (photographic film or image sensor) during
the process of taking a photograph. Exposure is measured in lux
seconds, and can be computed from exposure value (EV) and scene luminance.
Depth of Field:
In optics, particularly as relates to film and
photography, the depth of field (DOF) is the distance in front of and
beyond the subject that appears to be in focus. Although a lens can
precisely focus at only one distance, the decrease in sharpness is
gradual on either side of the focused distance, so that within the
DOF, the unsharpness is imperceptible under normal viewing conditions.
For some images, such as landscapes, a large DOF may
be appropriate, while for others, such as portraits, a small DOF may
be more effective.
A photographic lens (also known as objective lens or
photographic objective) is an optical lens or assembly of lenses used
in conjunction with a camera body and mechanism to make images of
objects either on photographic film or on other media capable of
storing an image chemically or electronically.
Zoom lenses, have a focal length that varies as
internal elements are moved, typically by rotating the barrel or
pressing a button which activates an electric motor. Commonly, the
lens may zoom from moderate wide-angle, through normal, to moderate
telephoto; or from normal to extreme telephoto. The focal length of a
zoom lens is not fixed; instead it can be varied between a specified
minimum and maximum value. Modern lens technology is such that the
loss of image quality in zoom lenses (relative to non-zoom lenses) is
minimal, and zoom lenses have become the standard lenses for SLRs and
DSLRs. This is different from only 20 years ago when, due to image
quality concerns, most professional photographers still relied
primarily on standard non-zoom lenses.Zoom lenses are often described
by the ratio of their longest to shortest focal lengths. For example,
a zoom lens with focal lengths ranging from 100 mm to 400 mm may be
described as a 4:1 or "4×" zoom. Typical zoom lenses
cover a 3.5× range, for example from 24 - 90 mm (standard zoom)
or 60 - 200 mm (telephoto zoom). "Super-zoom" lenses with a
range of 10× or even 14× are becoming more common, although
the image quality does typically suffer a bit compared with the more
traditional zooms. The maximum aperture for a zoom lens may be same
for all focal lengths, but it is more common that the maximum
aperture is greater at the wide-angle end than at the telephoto end
of the zoom range. For example, a 100 mm to 400 mm lens may have a
maximum aperture of 4.0 at the 100 mm end but only 5.6 at the 400 mm
end of the zoom range.
A wide-angle lens is a lens whose focal length is
substantially shorter than the focal length of a normal lens for the
image size produced by the camera, whether this is dictated by the
dimensions of the image frame at the film plane for film cameras
(film format) or dimensions of the photosensor for digital cameras.
A teleconverter is a secondary lens which is mounted
between the camera and a photographic lens. Its job is to enlarge the
central part of an image obtained by the objective lens. For example
a 2× teleconverter enlarges the central 12×18 mm part of an
image to the size of 24×36 mm. Teleconverters are typically made
in 1.4×, 2× and 3× models. The use of a 2×
teleconverter (or doubler) gives the effect of using lens with twice
the focal length. It also decreases the intensity of the light
reaching the film by the factor of 4 (an equivalent of doubling the
focal ratio) as well as the resolution (by the factor of 2).
Standard non-zoom lenses are called prime lenses or
simply "primes". Their advantage, in addition to typically
giving a better image quality, is that they are smaller, lighter and
cheaper than a zoom lens of the same quality. A prime lens may also
be "faster" and have a larger maximum aperture (smaller
f-number), so it can be used with less light (with the same shutter
speed), and can provide less depth of field in situations where this
Macro lenses are designed for extreme closeup work.
Such lenses are popular for nature shooting such as small flowers, as
well as for many technical applications. Occasionally, macro lenses
are used for close portraits.
In photography, a fisheye lens is a wide-angle lens
that takes in an extremely wide, hemispherical image. Originally
developed for use in meteorology and astronomy and called
"whole-sky lenses", fisheye lenses quickly became popular
in general photography for their unique, distorted appearance. They
are often used by photographers shooting broad landscapes to suggest
the curve of the Earth. Hemispherical photography is used for various
scientific purposes to study plant canopy geometry and to calculate
near-ground solar radiation. The focal lengths of fisheye lenses
depend on the film format. For the popular 35 mm film format, typical
focal lengths of fisheye lenses are between 8 mm and 10 mm for
circular lenses, and 15-16 mm for full-frame lenses. All the
ultra-wide angle lenses suffer from some amount of barrel distortion.
While this can easily be corrected for moderately wide angles of
view, rectilinear ultra-wide angle lenses with angles of view greater
than 90 degrees are difficult to design.
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