You can control depth of
field to make the background blurry (out of focus)
Depth of field means
that more than just one spot in your picture looks sharp.
When you focus on a subject
(when you set your camera for the distance from the camera to the
subject) the subject itself will be quite sharp. Things farther away
will be less sharp; things closer will be less sharp. You have some
control over what's going to be sharp and what's going to be fuzzy,
mostly by choosing the focal length of your lens and by choosing the
aperture (lens opening).
A "shorter" lens (one with
a wider angle of view) has more depth of field. A longer lens has
less depth of field.
Using a smaller f-stop such
as f22 increases depth of field. A larger lens opening such as f2.8
has less depth of field.
In the photos below, I
stood closer to Andy while using the shorter focal length (70mm). I
stood almost 3 times farther away when using the longer focal length
(200mm). That way his head size remained about the same.
|Tamron 70-200mm f2.8 lens set at
70mm focal length and f22 aperture.
||Tamron 70-200mm f2.8 lens set at
200mm focal length and f2.8 aperture.
Setting the aperture - the lens opening on
your camera - wide open will reduce the depth of field, making the
background more blurred. Using a longer focal length will also
reduce the amount of background detail.
You'll find it easiest to do this when you set
your camera's mode dial to the A
setting. "A" stands for Aperture Priority - you
set the lens opening and the camera chooses the right shutter speed
The smaller the number, the larger the
opening: that is, f4 is a larger opening than f22 and therefore has
less depth of field. That's because the f number
is actually the denominator of a fraction. f22 means the lens is
open 1/22nd as big as the lens is long.
When I took the second photo I moved almost 3
times farther back but zoomed in to keep the head size about the
same. Big difference, isn't there?
We go into some detail about this in our
Digital 201 class.