By
Marc B
Last
week we introduced beginners to shutter speed. This week (in Part 2 of the
Introduction to Photography Exposure Terms), we’re introducing aperture.
Using
these two settings effectively, along with ISO settings, are key factors in
creating the type and style of photograph you want. Think about the outcome you
want and adjust your settings. Experimentation is the best way to learn what
works, and most importantly, what works for you. So start shooting!
Aperture
There
are two reasons to adjust aperture settings. These are, to control the amount
of light in your photographs, and creating your desired depth of field in each
shot.
Light
The
aperture or ‘f stop’ refers to the opening inside a lens that controls how much
light passes through the lens to the sensor.
In most lenses this is variable so the photographer can control the
light with a high degree of accuracy, choosing if they want a brighter or
darker photograph.
The widest aperture of a lens is usually
written on the front the lens, and is usually shown as, 1:2.8. This means that the
largest aperture on the lens is f2.8.
On
some zoom lenses it may be expressed as something similar to, 1:3.5-4.6. This means
that at the widest focal length of the lens the largest aperture is f3.5 and
when you zoom all the way in, the largest aperture will be f4.6. The different representation of the aperture
on a zoom lens is because the lens itself absorbs light as it is extended or
‘zoomed in’.
Depth of Field
Controlling
the area of apparent sharpness in an image is referred to as the depth-of-field
(dof) in an image. A large aperture (which
is achieved by selecting a small number ie. f2.4) will give a shallow depth of
field to an image, and a small aperture (which is achieved by selecting a large
number ie. f22) will give a deep depth of field.
In
the graphic below the relative sizes of the apertures are shown. At f22 the image will have apparent sharpness
from front to back. At f1.8 the image
will have a narrow band of sharpness, or a shallow depth of field.
Examples
The
first image is shot with a large aperture of f2.8 and you can see how the
depth of field drops off quickly and the image loses sharpness.
The
second image was shot with a small aperture of f22 and the depth of field
is now very deep and there is detail a lot further back into the image.
Keep
in mind that if you want the entire image to be sharp you need to use a small
aperture (choose a large ‘f stop’ number).
If you want to achieve a shallow depth of field, use a large aperture,
such as f2.4 or f1.8.
Experiment
and have fun!
Next
week, Part 3 of our ‘Introduction to Photography Exposure Terms’ will be on
ISO.
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