Autofocus
Unlike the cameras further up Nikon’s DSLR range that have 51 AF points, the D90 has 11 AF points, with just the central one being a cross-type. However, it still has four methods of selecting the active AF point: Single point AF, Dynamic Area AF, Auto Area AF and 3D Tracking AF.
The 3D Tracking AF mode uses the 420-pixel RGB sensor and Scene Recognition system to gather and interpret colour information to help recognise the subject and keep track of it as it moves around the image frame. Helpfully, the active AF point can be illuminated to make it easy to see whether the subject is being tracked.
Nikon’s 3D tracking is very effective when the subject is a different colour from its background. However, it’s not especially helpful when photographing team sports, as having numerous players in the same colour can cause some confusion. In these instances Dynamic Area AF mode, in which the user selects the starting AF point and the camera tracks the subject automatically, selecting the AF points it calculates to be appropriate, or the entirely automatic Auto Area AF mode, may be of more use.
Alternatively, the D90 also has a Single point AF mode, which uses one AF point to adjust the focus in continuous focus mode. Like the Canon EOS 550D’s continuous AF (AI Servo) mode, this option works well and does a good job of keeping the subject sharp provided the user can keep the AF point over the subject. Thanks to the fact that the AF points of the D90 are larger than those in the EOS 550D, I found it easier to keep a point over the subject with the Nikon system.
Both AF systems perform well, and although there were a few occasions when the EOS 550D’s AF system was able to bring a subject into focus when the D90’s could not, by the end of this test I had a little more confidence in the Nikon system than the Canon one.
The EOS 550D has smaller AF points and is better able to identify small details and bring them into sharp register, but in its continuous mode it is also more twitchy. This may be an advantage with fast-moving subjects travelling along a predictable line, but with other subjects it can mean unnecessarily dramatic shifts in focus. When photographing a local running race I was able to get decent shots with both cameras, but it seemed a little easier to do so with the D90.
It takes a little while to get to know the Nikon D90’s AF system, but it is more versatile than the EOS 550D’s and it helps make the Nikon camera a better choice for keen sports or wildlife photographers.
Image: Although it is possible to shoot sport with the Canon EOS 550D, it is a little easier with the Nikon D90, especially once the more flexible AF system has been mastered
