Four AF modes and focus pre-determination function help photographers get the most out of the new AF system.
The new AF system seems to have a full complement of functions. Please explain how it is actually used.
With as many as 11 focus sensors, an AF system can sometimes focus on subjects that you don't want to focus on, such as when your subject is not centered in the image area. So to remedy that, with the D2H you can select among four AF modes. Specifically, "Single Area AF" allows you to select one focus area to be used, "Dynamic AF with Focus Tracking and Lock-on™" automatically shifts the camera from one focus area to another to keep track of a moving subject, "Group Dynamic AF" allows you to select one of the five focus area groups, which are comprised of various configurations of the 11 focus areas, and "Closest Subject Priority Dynamic AF" automatically selects the focus area according to the closest subject to the camera. Users can select among these four modes according to shooting conditions, for superior results regardless of the situation.
Does the "Group Dynamic AF" mode debut with the launch of the D2H?
Right. "Single Area AF" and "Dynamic AF" modes have been available in the D1H. The new "Group Dynamic AF" mode divides the 11 focus areas into five focus area groups: top, bottom, left, right and center. You can select one among these five for focusing. The subject position you would like to focus on can be limited roughly, but still within a wider focus area, which makes it much easier to create the desired composition. On the image area, the selected focus area group is highlighted in red for easy confirmation.
Does this boil down to quick focusing and good composition at the same time?
Certainly. To see how truly effective this mode is, consider this gap it fills in: The camera can focus on a subject you don't want to focus on with "Closest Subject Priority Dynamic AF," but the subject can fall out of the AF sensing area if you use "Single Area AF."
I see. Now, high speed is required to focus on a moving subject, is that right?
- Nikon's unique overlap servo method drives the focus action of AF system and lens simultaneously, for fast, accurate AF operation.
Definitely. You may notice the number "2000" in the name of this AF system. It indicates the number of pixels the sensor has. The F4's sensor has 200 in its name, meaning that the D2H has 10 times as many pixels, so processing capability has been improved accordingly. The D2H offers 120ms per frame and can be used to shoot up to 8 frames per second. But if the lens cannot accommodate such high speed, then this specification is meaningless. Which makes the technology to drive the lens properly really important. High-speed shooting also requires higher function to focus on moving subjects. For example, when you take a picture of a sprinter in a short-distance race, the subject continues to move fast after the moment of shutter release, so there must be a difference in time, even if it represents just a moment, between when the lens focuses on the sprinter and when the shutter opens, along with a corresponding gap in distance. So it cannot help but delay AF. To solve this problem, the D2H predicts the movement of the subject on the signals sent from the lens to the camera body and drives the lens in predetermining focus.