Autofocus
Images: When shooting at 10fps, the continuous AF had no problem keeping up with the subject
Like the metering system, the D4’s AF system has also seen some improvements. The AF module itself is an adaptation of the Multi-CAM 3500 FX unit that was previously found in the D3, D3S and D700. One of the main upgrades is its performance in low-light conditions, with Nikon claiming that the camera can now focus in as little as -2EV of light – the equivalent of shooting by the light of a full moon.
The increased sensitivity of the AF sensor isn’t just an advantage when light is in short supply. All 51 AF points of the D4 work at an aperture of f/5.6, while the 11 centre points, including a cross-type sensor, can work at f/8. This is useful for sports and wildlife photographers, as it allows an f/4 lens, such as the Nikkor 600mm f/4G ED VR AF-S or the 500mm f/4G ED VR AF-S, to autofocus when used with a 2x teleconverter, creating 1,200mm f/8 and 1,000mm f/8 lenses respectively. It will also allow photojournalists to travel light and use a 200-400mm f/4 lens and teleconverter to cover a 200-800mm range.
Using the D4 at night under streetlights, I found that the AF performs very well with a Nikkor 24-70mm f/2.8 lens. Even when pointing at objects that are almost entirely in shadow, the D4 still focuses quickly and accurately. The D3S is no slouch in low light, but of the two the D4 was faster and more accurate, whereas the D3S had to hunt a little more often for the focus point and occasionally just gave up. In fact, for focusing in low light, the D4 is the most efficient camera I have come across. It really is impressive.
The new AF button, taken from the D7000, makes it far easier to change the number of focus points in use, or to switch to 3D matrix metering. All of this can be done without looking away from the viewfinder. Initially, I was concerned it might take longer to use the new AF switch to change from continuous to single AF and vice versa, but once familiar with the arrangement I found it faster than the previous system used on the D3S.
As you would expect, there are many different ways in which the AF system can be set up to suit the demands of different photographers, and it is worth spending time fine-tuning these settings rather than relying on the default configurations. For example, the response time of focus tracking can be changed. Setting this to its fastest system can help when photographing the sort of sports characterised by sudden or irregular movements, such as football matches. Likewise, it can be slowed, which will be more useful for tracking subjects that move at speed in a regular direction, such as a racing car.
Overall, the AF is superb. There is a difference in speed and accuracy compared to the D3S but it is only really in low light or when photographing a very fast-moving subject that this is particularly noticeable.
