Camera Controls
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:
Foucs
|
The position of a viewed object or the
adjustment of an optical device necessary to produce a clear image: in focus;
out of focus
|
Aperture
|
Adjustment of the lens opening,
measured as f-number, which controls the amount of light passing through the
lens. Aperture also has an effect on depth of field and diffraction – the
higher the f-number, the smaller the opening, the less light, the greater the
depth of field, and the more the diffraction blur. The focal length divided
by the f-number gives the effective aperture diameter.
|
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
|
raditionally 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.
The higher the ISO number the greater the film sensitivity to light, whereas
with a lower ISO number, the film is less sensitive to light. A correct
combination of ISO speed, aperture, and shutter speed leads to an image that
is neither too dark nor too light, hence it is 'correctly exposed', indicated
by a centered meter.
|
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 (normal, long focus, wide angle, telephoto, macro, 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.
No comments:
Post a Comment