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Autofocus (con' t)

AF functions: Nikon D3S and Canon EOS-1D Mark IV

As an initial point of comparison, it's interesting to see how Canon and Nikon have arranged the AF system and associated options in the EOS-1D Mark IV and D3S. Overall, the two systems include very similar options and capabilities, conveyed using slightly different terms. The major difference is how the two systems are configured and accessed. Compared to the Canon EOS-1D Mark IV the D3S's AF system is considerably easier to 'just use'. This is largely because although it offers similar levels of customizability, the most important permutations of the D3S's AF system are changed using physical switches, as opposed to press-and-scroll interfaces and/or custom functions.

The following table assumes the cameras are being used in continuous drive and continuous/servo AF mode.

Canon EOS-1D Mark IV

Nikon D3S
To switch between a single, specified AF point and letting the camera have its choice of points (Auto Selection), you press the AF point selection button then rotate the main control dial until the perimeter AF points light up in the viewfinder. To switch between using a single, specified AF point and letting the camera have its choice of points (Auto Selection), you flick the AF point mode switch on the back of the camera to its top position.
The number of selectable points can be limited from all points to 19, 11, or one of two arrangements of 9 points using C.Fn III-10. The number of selectable points can be limited from all points to 11 using Custom Setting a8.

Getting the camera to consider surrounding points or track a subject is set in Custom Function III-8.

In the last option (All 45 points area) the camera will consider the 18 surrounding AF points and select a new AF point if it believes the subject has left the selected point.

This menu item is the only way of changing the number of considered points and is the only way of stopping the camera considering other AF points.

Getting the camera to consider surrounding points or track a subject is defined in Custom Setting a3.

In the last option (51 point 3D tracking) the camera will consider distance and color and select a new AF point if it believes the subject has left the selected point.

The Fn button can be set to change the number of considered points without re-entering the menu. The AF point mode switch can stop the camera considering other AF points.

If the distance to the object in the selected AF point changes (the subject leaves the AF point or another object appears in front of the subject), Custom Function III-2 defines how long the camera waits before re-focusing to the new distance.

If Custom Function III-4 is set to 0 (AF point priority), the camera will automatically re-focus to the originally selected AF point if something passes in front of the subject.

If the distance to the object in the selected AF point changes (the subject leaves the AF point or another object appears in front of the subject), Custom Setting a4 defines how long the camera waits before re-focusing to the new distance.

If Custom Setting a4 is set to off, the cameras will automatically re-focus to the originally selected AF point if the distance changes suddenly.

Custom Function III-3 dictates whether the camera prioritizes focus or speed. A different priority can be specified for the first frame and another for the other shots in a burst. Custom Setting a1 dictates whether the camera prioritizes focus or speed. The same option is applied to all images in a burst, with an option that aims to offer a balance between the two requirements.

Continuous AF Performance

Anyone who has shot sport and action with a D3 or D3X will encounter no surprises when using a D3S, since performance is identical to the earlier cameras. As we've already stated, we don't claim to be experts in this field, but from analyzing the hundreds of images shot with the D3S at various sports events, we are confident that we, rather than the camera, are the consistent limiting factor in terms of our overall hit rate.

The continuous AF of the Nikon D3S didn't deliver 100% focused images in every situation in which we used it, but it is astonishingly capable, and proved itself when shooting a range of different events. From the bright, contrasty afternoon sunlight of a rugby (which, for our American readers, is a bit like American Football) match to the dark, flat conditions of floodlit football (which, conversely, is not a bit like American Football) the D3S consistently displayed what we consider to be excellent performance. The only time when we really felt the need to meddle with the more technical AF custom options was when shooting with a TC-17E teleconverter on the new AF-S Nikkor 70-200mm f/2.8 VR. With this combination we found that setting csm a4 to 'short' rather than the default 'normal' speeded up AF responsiveness when tracking.

Taken as a whole, we are very impressed by the D3S's capabilities. Not every frame that we shot is in focus, by any means, but after considerable experimentation with the various AF modes and custom function permutations, we are confident that the D3S has what it takes to tackle almost any situation. Compared to the Canon EOS 1D Mark IV (which we tested alongside the D3S with as near-parity of lenses as possible), we consider the D3S to be simpler to set up and use, but once both cameras were configured properly, both provided us with excellent results. For more detailed analysis of the 1D Mark IV's AF, watch out for our in-depth test, to be published shortly.

AF tracking/stability example

In this sequence of 10 images, the D3S was set to release/ priority (the default option of csm a1), in continuous AF mode. All 51 AF points were activated in 3D AF tracking mode. The camera has locked immediately to my target, and as you can see, it has stuck with him even when a second player enters the frame. As the scene dissolves into a mess of bodies in the final two frames, everything remains in sharp focus. We wouldn't recommend employing 3D AF tracking in all instances, because more than one subject of the same color and contrast in the frame can confuse the system. It has worked very well here though, almost certainly because the background is relatively uncluttered and free from moving elements.

 

 

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Barney Britton
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