If you already know what depth of field is and how to control it, the
important point to get from this primer is that a digital camera has
more depth of field at the same f/stop than a 35 mm camera. It is
about a 5 stop difference for most cameras, and as low as a 4 stop
difference for cameras with larger sensors, like the Olympus
IF YOU'RE NOT 100% SURE about what Depth of Field is,
read on ...
Everybody has probably seen photographs in which
every element from foreground to background is in sharp focus, and other
pictures in which only the subject is in sharp focus while everything else
is blurry. The first picture is said to have more depth of field
than the latter, which has shallow depth of field. For those that don't
know, depth of field, or DOF, is how deep the area in focus is,
when you focus on a given subject. It's a very powerful artistic tool.
You can use your depth of field to make something in the foreground in
focus, and blur out the background, thereby bringing more attention to
your subject. Or you can open your depth of field way up and put your
significant other and that mountain 10 miles behind her/him all into
sharp, startling, crisp focus.
Look at the picture of dummy-X
above: he's in focus, but the ceiling and background behind him are not.
That means the depth of field (DOF) is narrow and it's obviously
centered on him.
With Erni, though, on his pedestal, his background is almost as
in-focus as he is. The DOF is a bit deeper or wider.
really wide DOF might mean that grandma standing 5 feet away from you is
in focus, and so also is the tree 50 feet behind her. But a narrow DOF
might mean that even though you've focused sharply on the tip of grandma's
nose, her eyes, only an inch behind, are slightly out of focus.
does one control this? By changing your aperature. In general, the bigger
the aperature, the narrower the depth of field. (Don't know what an
aperature is? Click here). The opposite is also true: the smaller your
camera aperature, the wider or deeper your DOF.
Easy enough. Now
here's the confusing part for a lot of people. A smaller number is a
bigger aperature. Got that? An aperature of 2.8 is a BIGGER
hole/opening than an aperature of 16. Why? Because it's really a fraction
and they've left out the numerator. Just like 1/2 is bigger than 1/16.
Same thing. Still with us?
Now back to digital cameras. Since they
use a smaller area to capture the image than the 35mm film rectangle, they
give more DOF at the same aperature. Because remember, the smaller the
opening, the deeper the DOF. In other words, if you take a 35mm camera and
set the same f/stop as your digital, point them both at the same thing,
more will be in focus from front to back in the scene with the digicam. As
a rule of thumb, the DOF on a digicam is the same as the
DOF on a 35mm set 5 stops smaller.
What does that mean? Well, take a look at your aperatures on the
camera. If you've ever noticed, they seem to go in certain consistent
steps: 22, 16, 11, 8, 5.6, 4, 2.8, 2.0. Each one of those steps is an
f/stop, and it basically means, going from left to right, twice as much
light is being let in at each step. In other words, f/16 lets in twice as
much light as f/22. Better cameras give you more in-between f/stop
So if you set your digicam aperature to 2.0, and count 5 steps higher
(i.e. to the left), you'll see the equivalent aperature on a 35 mm camera
is 11. If you have a 35mm camera you can look at the DOF marks on the
lens and you'll know exactly how much depth of field, in both meters and
feet, you would then have.
What happens if you set your digicam aperature to f/16? Start
counting steps to the left and you run out right away. Basically this
means that setting your digicam to f/16 though gives you a much larger,
deeper DOF than you could ever get with a 35 mm camera. This can be
great for getting lots of stuff in focus. However, the downside is if you
want really shallow, or narrow DOF, it's a lot harder, because it's always
deeper, not narrower, thanks to those small digicam sensors.
best thing to do to really grasp this is set your camera up pointing at
something, and take a bunch of shots of that same thing, changing the
aperature each time, and watch how your picture changes. Best way to do
this is use aperature-priority mode (A mode), if your camera has it.
That way, the camera will automatically change the shutter speed to
compensate for the changes in amount of light you're letting in, and all
YOU have to worry about is the aperature and the depth of
- Kollin B., magnetic9999
|At this wide aperature (f/2.8), Erni can be seen
sharply, running from dummy-X, who's very
|At this intermediate setting (f/5.6), dummy-X is
a lot sharper, yet his shadow and the blinds are still
|Here's a very narrow aperature (f/11). Now
everything is in focus, including the blinds upon which the dummy's
(nothing personal) shadow is cast.