Aperture
Aperture being one of the
three main elements in photography while other two being shutter speed and ISO,
it can be used to control the overall exposure. Aperture determines the amount
of light entering to the camera by varying the diameter of the iris. For
example if the iris is wider, more light can go through to the camera and if
the iris is narrower, relatively small amount of light can go through.
Figure 1.0 lens with high and low aperture
The F-Stop value (Measurement of Aperture)
Figure 2.0 f-stops and
aperture.
How Aperture Determines the Depth of Field
Aperture directly involves
in depth of field which is in focused objects in a photograph. For example if
the f-stop is high as f/32 then all the objects in the photograph will appear
focused, and if the f-stop value is low like f/1.4 then the focused objects
will appear sharp but background objects will appear blurry. A single
photograph means series of layers capturing at once. Depending on these layers,
the depth of the photograph can be visualized.
Figure 3.0
Low f-stop photograph and a high f-stop photograph
In figure
3.0 we can see that photograph on the left has most layers blurred out and only
the object in-front appears to be sharp. This is known as a shallow depth of
field because the background of the image cannot be visualized.
The photo on
the right has more layers focused and sharp so the details of the each layer
are clearer. This can be identified as an image with a higher depth of field.
How Aperture Controls the Bokeh effect
The term 'Bokeh' comes from
the Japanese word 'boke' which means blurry. The effect of Bokeh is considered
to be the soft blurry background that you achieve when capturing a subject. For
a good Bokeh photograph, your lens should be set in high aperture position and
focus on an object, Bokeh is highly dependent on the aperture, so in order to
obtain more Bokeh effect out of the
picture you need to have
high aperture lens. For instance f2.8-f4.0 lens can give you a reasonable Bokeh
effect, but for a good quality blurry background or Bokeh you may need f2.8 or
higher lens.
Figure 4.0
Bokeh example
As you
already noticed both the pictures in figure 4.0 are with shallow depth of
fields and only few layers appear out as sharp so both these pictures were
taken at higher aperture levels, hence the background is blurred.
Picture on
the left has Bokeh lights which happen to be the shape of the lens iris when it
is widely opened.
How to Use Aperture in Photography
Since we already know what aperture is and how to control
it, it is time to see when and where to use it. We can use shallow depth of
field to focus and direct the lenses in to a particular subject and this is
useful in object photography and portraits. If you are taking a landscape or a
scenery, in most of the cases you need all the layers sharp in other words a
deep depth of field. So when taking these kind of pictures it is better to use
small apertures (higher f-stop).
Lighting conditions are also affected by aperture, if the
lighting conditions are very good as in mid-day you can lower the lens aperture
allowing only small amount of light to go through the lens and take pictures
without being over exposed. Similarly in low light conditions such as at dawn
or at night you can use high apertures to get more light into the camera and
avoid being under exposed.
Actually, when controlling aperture levels, there are no
limitations and boundaries. It is always up to your imagination and therefor
based on the picture you take you can control the aperture level accordingly.
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