One
of the more complex parts of a camera’s operating system
is the Autofocus (AF) subsystem. The Multi-CAM 1000 AF system
was released for the first time in the Nikon
D200, so we’ll use that camera and its manual as
the base for this article.
To
really maximize the use of the Multi-CAM 1000, it’s
important that new users spend some time with articles like
these (and with the camera’s manual) until they have
a good grasp of how the AF system works. The initial time
spent studying will result in professional quality images
later.
The Multi-CAM
1000 AF system is not that hard to understand so why not get
your user’s manual, and your camera, and let’s
go over the autofocus modes in detail.
What is Multi-CAM 1000 Autofocus?
It’s
a significantly improved version of the Multi-CAM 900 autofocus
module found in the Nikon D100, D70, and D50 digital SLR (DSLR)
cameras. Where the Multi-CAM 900 was limited to Single Area,
Dynamic Area, and Dynamic Area with Closest Subject Priority
modes, the Multi-CAM 1000 adds another AF mode called Group
Dynamic. This mode gives you finer control over things like
sports photography, macro focusing, and selective area AF.
While
the Multi-CAM 900 had five AF sensors, the Multi-CAM 1000
gives us 11. It is very similar to the 11-sensor arrangement
in the flagship Nikon
D2x Multi-CAM 2000 system. So, you can expect professional-level
performance from Multi-CAM 1000 in the D200.
Why is
it called Multi-CAM 1000? The number 1000 represents the approximate
number of CCD contrast-sensing elements in the autofocus system.
With so many elements, it will autofocus in low to high light
levels and at high speeds.
A unique feature of the Multi-CAM 1000 in the Nikon D200 is
the ability to combine the 11 sensors into a 7-AF areas wide-array
arrangement. This gives you the ability to better follow moving
subjects like flying birds, race cars, or airplanes. We’ll
discuss the Focus Zone Selection (7-AF areas array) in a later
section of this article.
Now,
let’s consider the various parts of the Multi-CAM 1000
AF system, and how they work.
What is Focus Lock, and How Does it Work?
Let’s
start our exploration by looking at some basic information.
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 for your particular
needs.
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®.
We’ll talk more about them in a later section.
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. It does “lock on” to your subject though,
and tracks it until you take a picture.
So,
“Focus Lock” is simply the camera making a decision,
based on the fact that it has acquired a subject and is ready
for taking a picture.
Once
the camera decides that it is ready, something else comes
into play. It will capture images with two levels of focus
accuracy, according to how you have the AF “priority”
set in Custom Settings a1 and a2. The two priorities are “Focus”
or “Release.” We’ll discuss these in the
next section.
