Single-Servo Autofocus (AF-S)
In this mode, also called AF-S, focus is set once and remains at that setting until the
button is fully depressed, taking the picture, or until you release the shutter button with-
out taking a shot. For non-action photography, this setting is usually your best choice,
as it minimizes out-of-focus pictures (at the expense of spontaneity). The drawback here
is that you might not be able to take a picture at all while the camera is seeking focus;
you’re locked out until the autofocus mechanism is happy with the current setting. As
described in Chapter 9, you can set AF-S mode to use either focus priority (the default)
or release priority using CSM #a2.
When sharp focus is achieved, the selected focus point will flash red in the viewfinder,
and the focus confirmation light at the lower left will flash green. If you’re using Matrix
metering, the exposure will be locked at the same time. By keeping the shutter button
depressed halfway, you’ll find you can reframe the image while retaining the focus (and
exposure) that’s been set. You can also use the AE-L/AF-L button, as described in
Chapter 9, if you’ve set that button to lock focus when pressed. Because of the small
delay while the camera zeroes in on correct focus, you might experience slightly more
shutter lag. This mode uses less battery power.
Continuous-Servo Autofocus (AF-C)
This mode, also known as AF-C is the mode to use for sports and other fast-moving
subjects. In this mode, once the shutter release is partially depressed, the camera sets the
focus but continues to monitor the subject, so that if it moves or you move, the lens
will be refocused to suit. Focus and exposure aren’t really locked until you press the shut-
ter release down all the way to take the picture. You’ll find that AF-C produces the least
amount of shutter lag of any autofocus mode when set to release priority: press the but-
ton and the camera fires. It also uses the most battery power, because the autofocus sys-
tem operates as long as the shutter release button is partially depressed.
Continuous-servo autofocus uses a technology called predictive tracking AF, which allows
the D7000 to calculate the correct focus if the subject is moving toward or away from
the camera at a constant rate. (Automatic autofocus, AF-A, described next, also uses
predictive tracking when operating in AF-C mode.) It uses either the automatically
selected AF point or the point you select manually to set focus. As described in Chapter
9, you can set AF-C mode to use release priority (the default), or focus priority using
CSM #a1.
If you want to lock the focus point you’ve selected for a series of shots, rotate the focus
selector lock lever up to the L position. You can also temporarily lock the focus point
by partially depressing the shutter release, or pressing the AE-L/AF-L button (unless
you’ve redefined this behavior to some other controls in the Custom Settings menu).
Chapter 5 ■Mastering Autofocus Options 149