In this article Chip Clark explains the
fundamental photographic concept of Depth of Field, and gives
you a simple exercise to use to show you the theory in practice.
Once you done the table exercise with the apples, you can
move on to other things, all the time getting better control
over your camera's handling of DOF. A
digital camera makes practising both quick to do and inexpensive.
What is Depth of Field - Beginning
Photography Basics
At some point all beginning photographers are confronted
with certain technical aspects of photography that have
them either burning up rolls of film, or loading up memory
cards! Two in particular: Exposure (which
will be addressed in a different article) and Depth
of Field (or DOF) leave the newly shutterbug
bitten novice shaking their head, wondering what they
are doing wrong.
When I first started taking on an informal teaching
role with beginning photographers it was interesting
that the single most common question asked by them was: "How
do I make the background blurry and my subject sharp?" and
of course, "what do I need to do when I want everything
in focus?"
It's inevitable. If you desire to take your photography
to a higher level of quality, you will need to understand
what causes short and long depths of field, and especially
how to manipulate it to express your vision. Let's get
started...
First - what is a photograph with a short Depth of Field,
and what is one with a long DOF? Quite simply, a photograph
with only the subject in focus, and everything before
and behind it blurry, is a photograph with a short DOF.
An image with everything in the foreground to the background
sharp and in focus has a long DOF. With this highly sophisticated
formula I'm sure you can figure out what a medium DOF
is!
Why use a short DOF? When you reach this level
of being able to control exactly what you want in focus
(typically referred to as Selective Focus) in
your photograph you will have developed a dynamic tool
that will create powerful photographs! You will see this
used extensively in photojournalism - such as the photographer
focusing on one particular individual in a crowd of people.
Creative use of this tool certainly gives sustenance
to the term: A picture paints a thousand words!
Quite often you will see the use of a short DOF in glamour
portraiture. A classic example is when you see the model's
eye closest to the lens sharply focused, and the one
furthest is blurred. It's one of the most unique techniques
a photographer can utilize to convey her or his message.
What about a long DOF? Landscape photography
is the best example of the long Depth of Field in use.
Shooting images of seemingly endless vistas would render
a photograph worthless if only a small portion of the
'field' was in focus. Since you want virtually everything
from closest to farthest tack sharp - you will want to
shoot with a long DOF. You can see this utilized with
incredible results in the works of the greatest fine
art photographers such as Ansel Adams and Edward Weston.
But even when making photographs of spectacular scenes,
there will be times when your creative vision will want
to focus attention on a tiny, fragile flower amidst nature's
grandest formations. Developing these techniques will
arm you with that kind of photographic versatility.
So now that you understand what DOF is, how do
you make it work? This is where we begin
to get a bit technical, but it's important you understand
it. Since DOF will vary depending on the focal length
lens you are using, my examples will be in regards
to using a normal SLR lens in the 45mm - 70mm range.
To be able to manipulate DOF you must be able to
adjust the aperture (or F-stops) on your camera.
Most all SLR cameras that are even remotely modern
can do this by switching your mode to Aperture
Priority mode - or AV mode.
While I will not give a detailed explanation about aperture
in this article - the simplest way to understand is this: An
F-stop is the adjustable opening that controls how much
light coming through your lens hits the film or digital
sensor. The shutter speed is involved with this
as well, but for now let's stick with aperture. The F-stop
also controls the DOF of an image.
Older SLR camera lenses typically have the F-stop numbers
on the lens barrel. An older very basic lens may have
numbers around the aperture ring like: 2.8 - 5.6 - 8
- 11 - 16 - 22. These are the F-stops, or the aperture
opening settings.
More modern cameras are electronic and the F-stops are
usually seen at the bottom of the viewfinder. Contemporary
lenses usually have more F-stop settings available, such
as: 2.8 - 3.5 - 5.6 - 6.3 - 7.1 - 8 - and so forth, possibly
all the way up to 32.
To choose the DOF you wish to use for a particular shot
you need to understand this very basic concept: The
lower the F-stop number - such as 2.8, the shorter your
DOF will be. The higher the F-stop number - 22, the longer
the depth of field. To simplify it further -
making a photograph with F22 or higher is going to have
everything in the final image in focus. Shooting with
the aperture set at 2.8 is going to mean that only what
you specifically focused on is going to sharp.
Take a moment to absorb this because this basic concept
is the nuts and bolts of creating a quality photograph,
rather than just taking a picture. The very best exercise
you can do to practice this technique is to line up 3
objects - such as apples. Place them on a table about
2' apart lined up going away from you at just enough
of an angle so the first one isn't blocking the other
two. Place your camera about 3' from the first one, and
focus on the apple in the middle. Shoot several shots
- each one at a different f-stop, starting with the lowest
number (short DOF) and changing to the next higher f-stop
after each shot...all the way to the highest F-stop.
If your lens has an F-stop number as low as 2.8 you
will see that maybe only the forward surface of the apple
is in focus - everything from closest to furthest is
gradually very blurry. With each shot changed to a higher
F-stop number you will see more of the field in focus.
By the time you get to the highest F-stop setting, virtually
everything in the photo will be sharp and focused.
Most SLR cameras have a DOF Preview Button. If you use
it while looking through the lens at your scene - you
will see what the final image will look like. Only problem
is - the higher the F-stop number is, the smaller the
amount of light is let in. So it can be very difficult
to see because it will be very dark. After practicing
with these techniques you will not bother with the DOF
preview button. You will know how the image will be reproduced.
That is the mystery of Depth of Field in a nutshell! Yes,
there is more in-depth aspects of DOF - such as understanding
Hyper Focal Distance, and of course knowing that you
will get different DOF results with longer and shorter
focal length lenses. But understanding these basic DOF
concepts will revolutionize your photography, and give
you one more step up in photographic quality.
Chip Clark is a San Diego based professional
photographer, with over 20 years experience in landscape
photography, wildlife photography, sports photography,
and portraiture.
