The amount of light that enters to the camera's
imaging sensor (exposure level) plays a large role in
the quality of the image. The exposure can be
controlled mainly by two parts of a camera: the
Aperture and the Shutter. Perfect balances between
the settings of these two parts are essential to achieve
the desired quality and effect.
The aperture is the opening of the lens where light
enters before it goes to the imaging chip. It acts like
the pupil of a human eye that contracts to make the
opening larger and allowing more light to enter or
expands making the opening smaller thus reducing
the amount of light that enters to the eye.
In the camera the Aperture Opening is controlled by
the Iris which is composed of mechanically interlinked
overlapping blades that opens or closes as needed.
Aperture opening is expressed in F-values called Fstops. F-value is equal to the focal length of a lens
divided by the aperture's diameter.
A lens with a focal length of 100mm for example with
an aperture opening diameter of 36mm has an F-value
of 100/36 = 2.8. The aperture value will be expressed as
f/2.8 or F2.8. The same way, if the diameter of the
opening of the same lens is reduced to 25mm then the
F-value is 100/25 = 4, so the F-value is f/4.0 or F4.0.
This shows that the larger F-value means a smaller
Common F-values used by camera lenses today are the
following: f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16,
f/22, f/32, etc. The values are rounded off to these
numbers to make it easier to remember.
Each step of these values is called a "stop". Each stop
higher reduces the opening area by half, and as a result
allows only half as much light to pass through. f/4 for
example is one stop higher than f/2.8 so it offers only
half as much light than f/2.8.
Diagram of decreasing aperture sizes (increasing f-numbers)
for "full stop" increments (factor of two aperture area per
The aperture range of a 50mm "Minolta" lens, f/1.4-f/16
At f/16 the background is distracting
At f/1.4 the background is reduced to a
blur, but not all of the subject is in
The focal length of a lens is defined as the distance in
mm from the optical center of the lens to the focal
point, which is located on the sensor or film if the
subject (at infinity) is "in focus".
In photography, the focal length of a lens means the
magnification or telephoto power of the lens and is
expressed in the millimeters of the lens, like 100mm,
300mm, etc. The higher the number the higher the
magnification the lens will provide. At the higher
magnifications, it will be harder to hand-hold the
camera without getting a blurry picture.
The photograph shows a
focal length of about
36mm. This lens
magnification is great for
landscapes or large group
pictures. This focal length
also works great if you are
close to your subject and
want to include as much as
possible in the frame. Any
time you wish to include a
wide view of what you are
photographing, choose a
focal length between
20mm and 40mm.
Here the focal length is
75mm. This focal length is
good for cutting out some of
the distracting objects in the
background. While this lens
setting is not quite long
enough for a good portrait,
this setting would be good
for small groups or if you
want to include some
This photo shows about
125mm of magnification.
This length is good for
portraits. Move closer to
your subject and you can
easily fill your frame with a
pleasing head shot.
Here is a 300mm focal
length shot. Use this
setting to get right into
the action. This setting is
great for nature or sports
photography. With this
setting, you will cut out
most of the background
This photo shows 450mm
of magnification. This is
an example of an
extremely long focal
length. This length is
excellent for bird
photography and sports.
Use this length if your
subject is far away and you
cannot get closer.
The focal length of a lens is usually displayed on
the lens barrel. Pictured below is a Nikon lens
with a focal length of 50mm. The maximum
aperture is f/1.8 (also often written as, F1.8).
A landscape at 18mm, the white box marking 1/5 of the
width and height.
The same landscape at 90mm: the focal length is 5
times longer so the area marked by the white box fills
the whole scene
Zoom is the ability of a camera to magnify or de-
magnify an image to a certain range. A 3x zoom factor
indicates that the camera is capable of magnifying
from its lowest zoom value up to a point where the
image is three times its size.
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