Previous page Next page

Autofocus (cont.)

AF Functions: Nikon D3S and Canon 1D Mark IV

As a comparison, it's interesting to see how Nikon arranges its AF system and options. 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. The major difference is that on the Canon you can switch between manual AF-point selection and automatic point selection using external controls while the Nikon gives the additional option of engaging a dynamic AF point mode (where points other than the originally selected point are used).

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. Pressing the multi selector can be used to change between Auto and manual if C.Fn III - 11 is activated 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.

Performance

Whatever our thoughts about the way the system is configured, it's hard not to be impressed with its performance. We're not professional sports shooters and wouldn't claim to have tested the system to its limits (many of the Mark III's problems only came to light once the camera had been used extensively in very specific circumstances), but during our testing we shot a selection of sports in lighting ranging from stark winter sunshine to low-intensity minor-league floodlighting and found the Mark IV's ability to acquire and maintain focus was very good. Having set up the camera with advice from Canon, the (low) failure-rate in our photography was almost always down to a lack of experience of anticipating action in the events, rather than any lack of capability on the camera's part.

Following the issues surrounding the 1D Mark III there have, almost inevitably, been reports that the 1D Mark IV is also troubled. We didn't have any significant problems when shooting in really poor light, but the AF does lose a little of its 'snap' and immediacy, and seemed more prone to hunting than the 1D Mark III we tried it against (the Mark III's low-light focus being regarded as amongst the very best). Without knowing the precise details of how they were shot and how long the photographers had taken to get to know the new camera, it's hard to draw firm conclusions from these reports. We're not in a position to make a definitive statement but, having used the 1D Mark IV repeatedly alongside the Nikon D3S, we certainly wouldn't report any obvious problems and would be surprised if, with the correct setup, it doesn't prove itself to be as capable as the state of the art allows.

AF tracking/stability example

In this sequence of 11 images, shot over around 1.5 seconds, a player unexpectedly breaks loose from a maul and runs diagonally across the pitch (and hence away from my shooting position). The first shot is focused a fraction behind the player with the ball, but the AF very quickly locks onto him and holds him in focus, despite him leaving the central AF point at times due to my imperfect attempts to predict the speed at which I had to follow him with the camera. Even when he drops outside the central AF point, the camera continues to track him (it was set to consider the 6 AF points around the selected point, C.Fn III 8:2). It's only when one of the opposition players obscures him that the camera re-focuses (the speed with which it did so can be fine tuned with C.Fn III 2).

 

Previous page Next page
147
I own it
55
I want it
28
I had it
Discuss in the forums

Comments