WHAT
IS FOCUS LOCK?
Let’s start our exploration of the Multi-CAM 2000 system
by looking at some basic information that many of us may not
fully understand.
One
question often asked is, “What does it mean to lock
focus?” That's a great question since it involves how
the camera decides when a picture can be taken, and what AF
modes you’ll find most useful.
If
a subject is moving, the camera will use two technologies
to track it. They're called Predictive Focus Tracking®
and Focus Tracking with Lock-On®. More
about them later.
Using
these technologies, the camera detects that the subject is
moving in the few milliseconds that autofocus is in action.
According to whether it's in “single-focus” AF-S
mode (Single Servo AF) or “constant-focus”
AF-C mode (Continuous Servo AF) two distinct
events will occur.
Single
Servo AF: In this case, the autofocus system sees
subject movement and does not “lock” the focus
until the subject stops moving. When the subject stops the
focus “locks.” Once this lock takes place, the
little round green light comes on in the viewfinder, and autofocus
activity ceases. You must reactivate autofocus by lifting
your finger and reapplying pressure. The focus is truly locked
and will not try to follow your subject unless you refocus.
To follow a moving subject requires you to tap the shutter
button as the subject moves.
Continuous
Servo AF: When using this mode the autofocus never
“locks” at all. Your camera will capture images
with three levels of focus accuracy, according to how you
have the AF “priority” set. (Priorities: FPS
rate, FPS rate + AF, and Focus) We'll discuss these later
on.
Many
photographers use a method of shooting best called “Focus
and Recompose.” A good example of this is photographing
a couple of friends who are standing a couple of feet apart.
The photographer, using AF-S mode, moves his camera so that
the selected AF sensor is pointing at the face of one of the
friends. He locks the focus by holding pressure on the shutter
button, moves the camera to the composition that looks best,
and then snaps the picture.
As
long as the photographer holds pressure on the shutter button,
the camera will not try to refocus, since the focus is “locked.”
When he presses the shutter button the rest of the way, firing
the shutter, the camera will not try to refocus on the background
between the friends.
How
many of us have pictures of a perfectly focused background
with two friends blurred and out of focus? I'll never admit
it, but I sure do! (huh?) Using AF-S and the “Focus
and Recompose method” makes this problem unlikely to
happen.
So,
remember this. Once autofocus “locks” it stops
working until you release pressure from the shutter button.
This is perfect for non-moving subjects, or even slowly moving
subjects.
If
your subject never stops moving, is moving erratically, or
only stops briefly, AF-S is probably not the best mode to
use. Then AF-C is better, since it never locks focus and you
can better follow movement.
So,
“locking focus” simply means that the autofocus
system is finished doing its job, and is waiting for you to
conclude by taking the picture. This only applies to Single
Servo AF (AF-S) mode.
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