Depth-of-field refers to how
much of the photo is in sharp focus. This is affected primarily by the
size of the lens opening (aperture). All other factors being the same,
i.e., amount of light and camera-to-subject distance, the smaller the
lens opening, thr greater the depth of field will be. Compare the two
examples below. The photo on the left was taken using a large lens opening.
Notice how the front of the car is out of focus. On the right, the entire
car is in focus, because this photo was taken using a small lens opening.
A side note
about ISO/ASA (film speed) ratings...
also known as the ISO/ASA rating, also affects the aperture.
The higher the rating, the smaller the aperture needs to be
to get a proper exposure. This also holds true for the "digital"
film or memory cards used in electronic cameras, at least
the ones that allow you to manually select a virtual ISO/ASA
rating. This is a somewhat advanced territory, and won't be
discussed at length in this article, because other, more basic
techniques can achieve acceptable results.
how do you set things up? Most cameras allow you to chose between
automatic settings, and manual settings for shutter speed and aperture.
So if you camera has that feature, you'll want to manually set it
for the smallest possible aperture. There are two main factors that
now come into play: amount of light and shutter speed. Basically,
there's a ratio between the amount of light and the shutter speed.
The more light you have, the faster the shutter speed can be. This
is important if you're hand-holding the camera. Generally if the
shutter speed is less than 1/60 per second, it is very difficult
to get a photo that isn't blurred because of camera motion.
For this reason, I frequently
shoot photos of my models outdoors in full sunlight. This ensures
a high level of light, and the quality of the light appears more
realistic. Compare the two photos below. The one on the left was
taken indoors using artificial lighting. The one on the right was
shot outdoors, using natural light.
All well and good, you say,
except that it's the middle of January and there's a foot of snow on the
ground. Then it's time to shoot your photos indoors. Most cameras these
days have built in flash, which helps a great deal. Except that in many
cases, you'll have to forget setting the aperture manually and revert
back to the automatic settings. The advantage here is that in most cases,
using a flash will give you acceptable depth-of-field.
Or you can manually set the
camera for a small aperture, mount it on a tripod, and use whatever light
source you have available. This is a bit more tricky, because our old
nemesis "camera shake" comes back to haunt us. To get around
that you'll need to either use a remote shutter release (normally available
only on higher-end equipment) or use the camera's self-timer feature (if
it is so equipped). Here are a couple of examples, on the left, natural
room light, and on the right, using the camera's built-in flash.