unction and cameras
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.
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.
The
movie camera is a type of photographic camera which 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
movie camera takes a series of images, each called a "frame".
This is accomplished through an intermittent mechanism. The
frames are later played back in a movie 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 together to create the illusion of motion.[2]
In all but certain specialized cameras, the process of
obtaining a usable exposure must involve the use, manually or
automatically, of a few controls to ensure the photograph is
clear, sharp and well illuminated. The controls usually include
but are not limited to the following:
-
Focus - the adjustment to place the sharpest focus
where it is desired on the subject.
-
Aperture – adjustment of the
iris, measured as
f-number, which controls the amount of light passing
through the lens. Aperture also has an effect on focus and
depth of field, namely, the smaller the opening
aperture, the less light but the greater the depth of
field--that is, the greater the range within which objects
appear to be sharply focused. The current focal length
divided by the f-number gives the actual aperture size in
millimeters.
-
Shutter speed – adjustment of the speed (often
expressed either as fractions of seconds or as an angle,
with mechanical shutters) of the shutter to control the
amount of time during which the imaging medium is exposed to
light for each exposure. Shutter speed may be used to
control the amount of light striking the image plane;
'faster' shutter speeds (that is, those of shorter duration)
decrease both the amount of light and the amount of image
blurring from motion of the subject and/or camera.
-
White balance – on digital cameras, electronic
compensation for the
color temperature associated with a given set of
lighting conditions, ensuring that white light is registered
as such on the imaging chip and therefore that the colors in
the frame will appear natural. On mechanical, film-based
cameras, this function is served by the operator's choice of
film stock or with color correction filters. In addition
to using white balance to register natural coloration of the
image, photographers may employ white balance to aesthetic
end, for example white balancing to a blue object in order
to obtain a warm
color temperature.
- Metering – measurement of exposure so that
highlights and shadows are exposed according to the
photographer's wishes. Many modern cameras meter and set
exposure automatically. Before automatic exposure, correct
exposure was accomplished with the use of a separate
light metering device or by the photographer's knowledge
and experience of gauging correct settings. To translate the
amount of light into a usable aperture and shutter speed,
the meter needs to adjust for the sensitivity of the film or
sensor to light. This is done by setting the "film speed" or
ISO sensitivity into the meter.
-
ISO speed – traditionally used to "tell the camera"
the
film speed of the selected film on film cameras, ISO
speeds are employed on modern digital cameras as an
indication of the system's
gain from light to numerical output and to control
the automatic exposure system. A correct combination of ISO
speed, aperture, and shutter speed leads to an image that is
neither too dark nor too light.
-
Auto-focus point – on some cameras, the selection of
a point in the imaging frame upon which the auto-focus
system will attempt to focus. Many
Single-lens reflex cameras (SLR) feature multiple
auto-focus points in the viewfinder.
Many other elements of the imaging device itself may have a
pronounced effect on the quality and/or aesthetic effect of a
given photograph; among them are:
- Focal length and type of lens (telephoto
or "long" lens,
macro,
wide angle,
fisheye, or
zoom)
- Filters placed between the subject and the light
recording material, either in front of or behind the lens
- Inherent sensitivity of the medium to light
intensity and color/wavelengths.
- The nature of the light recording material, for
example its resolution as measured in pixels or grains of
silver halide.
