- Camera: Most SLR and
DSLR cameras provide the option of changing the lens. This enables the use of lens
that is best suited for the current photographic need, and allows the
attachment of specialized lenses. Film SLR cameras have existed since the late
1950s, and over the years a very large number of different lenses have been
produced, both by camera manufacturers (who typically only make lenses intended
for their own camera bodies) and by third-party optics companies who may make
lenses for several different camera lines.DSLRs became affordable around the mid-1990s, and have become
extremely popular in recent years. Some manufacturers, for example Minolta, Canon and Nikon,
chose to make their DSLRs 100% compatible with their existing SLR lenses in the
beginning, allowing owners of new DSLR's to continue to use their existing
lenses and get a longer lifespan from their investment. Others, for example Olympus, chose to create a completely new lens mount and series of lenses
for their DSLRs. The Pentax SLR camera K-mount system is backward compatible to all previous lens
generations from Pentax, including the latest digital SLRs like the K-5 and
K-r. A Pentax K-mount lens from the early 70s can be utilized on the newest
Pentax DSLR although it may not provide features that are included in newer
lenses (e.g. autofocus). There are a few exceptions from the MZ and ZX series
of Pentax film cameras that do not work with some of the older lenses.As implied by the above, lenses are only directly interchangeable
within the "mount system"
for which they are built. Mixing mounting systems requires an adapter, and most
often results in compromises such as loss of functionality (e.g. lack of
autofocus or automatic aperture control). Further, in some cases the adapter
will require an additional optical element to correct for varied registration
distances (the distance from the rear of the mount to the focal plane on the
image sensor or film). Adapters may not be available to bridge every
combination of lens mount and camera mount.
Photography: (derived from the Greek photos- for "light" and -graphos for "drawing") is the art,science, and practice of creating durable images by recording light or other electromagnetic radiation, either chemically by means of a light-sensitive material such as photographic film, or electronically by means of an image sensor.[1] Typically, a lens is used to foced exposure. The result in an electronic image sensor is an electrical charge at each pixel, which is electronically processed and stored in a digital image file for subsequent display or processing.us the light reflected or emitted from objects into a real image on the light-sensitive surface inside a camera during a tim
Exposure: Camera controls are interrelated. The total amount of light reaching the film plane (the 'exposure') changes with the duration of exposure, aperture of the lens, and on the effective focal length of the lens (which in variable focal length lenses, can force a change in aperture as the lens is zoomed). Changing any of these controls can alter the exposure. Many cameras may be set to adjust most or all of these controls automatically. This automatic functionality is useful for occasional photographers in many situations.
The duration of an exposure is referred to as shutter speed, often even in cameras that do not have a physical shutter, and is typically measured in fractions of a second. It is quite possible to have exposures from one up to several seconds, usually for still-life subjects, and for night scenes exposure times can be several hours. However, for a subject that is in motion use a fast shutter speed. This will prevent the photograph from coming out blurry.[29]The effective aperture is expressed by an f-number or f-stop (derived from focal ratio), which is proportional to the ratio of the focal length to the diameter of the aperture. Longer lenses will pass less light even though the diameter of the aperture is the same due to the greater distance the light has to travel; shorter lenses (a shorter focal length) will be brighter with the same size of aperture.
The smaller the f/number, the larger the effective aperture. The present system of f/numbers to give the effective aperture of a lens was standardized by an international convention. There were earlier, different series of numbers in older cameras.
