Depth of field refers to the area of an image that is in sharp focus versus out of focus or blurred. Controlling depth of field through aperture allows photographers to emphasize subjects by blurring backgrounds. A smaller aperture number (larger opening) produces a shallower depth of field with a blurred background. Choosing lenses with wider maximum apertures allows shooting in lower light and more dramatic blurring of backgrounds. Controlling depth of field through aperture adds impact to photographs.

2. Understanding Depth of
Field
0 When done well, a photograph that has good control
over the depth of field can add dramatically to the
impact of the picture.
0 When we are talking about depth of field, what we are
referring to is a shot were the main subject of the
picture is in sharp focus but other elements in the
picture are blurred or out of focus.

3. Understanding Depth of Field
What do we mean by controlling
depth of field (DoF)
0 Two key terms to learn here are focal plane which is the
area of the image that we want to have in sharp focus and
bokeh which is the out of focus sections.
0 This is the effect where the subject is in sharp focus but the
rest of the image is slightly out of focus.
0 The effect is referred to as bokeh. The more bokeh, the more
dramatic the blurring effect.

4. Understanding Depth of Field
Understanding Aperture
0 If you have a fully automatic point and shoot then you
will not be able to achieve the effect you want.
0 Being able to control the depth of field is not very easy
on lower end cameras as you need to be able to shoot
in either an aperture priority mode or in a full manual
mode.

5. Understanding Aperture
Diagram of decreasing aperture sizes

6. Understanding Aperture
0 The aperture setting is the size of the opening that is
used to let light into the camera and onto the sensor.
0 The size of the opening is measured is F-stops.
0 The confusing part is that the larger the aperture
setting, the smaller the hole that will be used to take
the picture

7. Understanding Aperture
0 The reason why lenses with a very large aperture (smaller
f-stop number) are more expensive is because the lenses
require more engineering and typically use better and
more complicated lens elements.
0 The other side effect of getting a lens with a small f-stop
number is that the smaller the f-stop, the more light will
come in per image thus allowing you to shoot in lower light
conditions.
0 A lens with a f/1.8 can shoot well exposed pictures in a
situation that is much darker than an f/4.0 lens could shoot
in.

8. Why Control DoF?
0 The simple answer is mood.
0 Quite often, the background of an image may be
distracting from the subject matter, think of a bride
standing in front of a wall of flowers.
0 In this case, the bride is obviously the main subject
and anything else may distract from the subject, by
blurring out the flowers behind the bride, you can
retain some of the color and texture without the
detail, adding a much more dramatic feel to the image.

9. Choosing Lenses
0 When choosing a new lens, once you decide once you decide the
focal range you are looking for, then you go for the lens with the
largest aperture (again, lowest number) that you can afford.
0 A common misconception with new photographers is that a lens
labeled with a single aperture will only do that aperture.
0 The labeling denotes the maximum aperture at the listed focal
length, So if you have a 70-300 f/4.0 – f/5,6, then your maximum
aperture at 70mm will be f/4.0 but will shrink to f/5.6 at 300mm
0 Whereas a 70-200 f/2.8 can maintain f/2.8 throughout the entire
focal range but can also go to the minimum aperture of you
camera (often f/22 or lower),

10. Now that you have these basics
down, you should be able to tell
that the faster (smaller f-stop
number) the better able the lens is
to shoot in darker conditions and
when used at the lens’ maximum
aperture, the more pronounced
the bokeh effect will be

11. Source:
http://cameradojo.com/201
1/06/09/understanding-
depth-of-field/