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Multi-CAM 2000 AF Sensor Module

The D1H made its debut in 2001. The D2H digital SLR for professional use was launched last November. We spoke to a designer who devoted his career at Nikon to developing this camera's innovative AF system.

UCHIYAMA, Shigeyuki
5th Design Section, Development Department, Development Division,
Imaging Company
Nikon Corporation
PROFILE:
Born in 1963. Spent his company career focusing on development of Nikon AF systems of most Nikon AF cameras launched after 1987. Has a U2 for most of his personal use, but uses an FM3A manual focus camera to enjoy more imaginative shooting in earnest. As he says, "There is no formula for AF system development. For that, we depend only on experience. I hope to pass the expertise that I have accumulated on to the younger generation."

The debut of the D2H camera introduces Nikon's new Multi-CAM 2000 AF Sensor Module AF sensor system, with unique functions for professional-level use.

Like the D1H which preceded it, the D2H is a digital SLR camera that is preferred by many professional photojournalists and other photographers. Please explain what is perhaps its greatest feature: a new AF system that allows a photographer never to miss the best shooting opportunity.

The D2H: a supremely reliable, high-performance, professional-caliber digital SLR camera.

UCHIYAMA, Shigeyuki:

We developed a new AF sensor called Multi-CAM 2000 AF Sensor Module exclusively for the D2H. Basically, it is superior in three ways: First, it has an 11-area sensor. Earlier Nikon AF systems featured nothing more than a five-area sensor, so the new AF sensor marks a radical improvement, covering a wider image area. Second, nine of the sensor's 11 areas, that is, the ones between the sensors at either end are cross-type sensors, ensuring razor-sharp focus even in shots featuring vertical or horizontal stripes. Third, it features a wider area of defocusing detection, so the lens can detect appropriate focus points without delay.

Which of those three points is most important?

The second point, involving cross-type sensors. Naturally, sensors that could detect horizontals as well as verticals offer better results, so cross-type sensors have been introduced in cameras made by Nikon as well as other manufacturers, much to users' satisfaction. But, technologically, it is not easy to feature a cross-type sensor, so most manufacturers use it only around the center of the image area. The Nikon F5 camera launched in 1996 features three cross-type sensors on the center and two other points horizontally adjacent to the center. Now, with the D2H, we succeeded in positioning cross-type sensors on more points, for vertical and diagonal directions.

Advanced high-speed, high-precision 11-area AF system featuring 9 cross-type AF sensors delivers quick response and sharp focus under all shooting conditions.

I see. What kind of technology was required to feature cross-type sensors?

In shooting, images from the lens are detected by CCD, a kind of image sensor. A conventional camera has only one CCD, which leads ultimately to the equivalent of optical overload. So we decided to install in the D2H three CCD sensors to make cross-type sensors work properly.

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.