Shooting mode information
The autofocus system will be the area of the 1D Mark IV that is most heavily scrutinized, following the problems with 1D III. The system is, depending on how you look at it, either phenomenally customizable or overly complex. The benefits of this level of customization are that it can be tailored very precisely to the subject you want to shoot, or to how you want or expect it to behave. The downside is that, although the defaults have been chosen to give good performance in a broad range of situations, it will take a little reading and experimentation before you learn to tailor it to your style and chosen subject.
Auto Focus system overview
The EOS-1D Mark IV uses a new 45-point AF sensor with 39 cross-type AF points (up from 19 on the previous model). However, they only behave as cross-type AF points when using a lens with a faster maximum aperture than f/2.8 and when selected manually. If automatically selected by the camera, only 19 of the points act as cross-type AF points (the same 19 that were selectable cross-type on the Mark III). With f/4 lenses, only the center point acts as a cross-type point, will all points reduced to horizontal sensitivity when using f/5.6 lenses or slower.
Interestingly, all 39 points remain cross-type when using Canon's 17-40mm f/4 L, 24-105mm f/4 L IS and various combinations of fast telephoto lenses with teleconverters, despite their maximum apertures being smaller than f/2.8.
In order to more quickly get to the AF point you wish to select, the number of active points can be limited, using C.Fn III-10. Changing this option doesn't limit the number of points the camera itself will select (in automatic selection mode) but does allow you to choose from the following arrangements (available points in red):
|All 45 points (non-cross-type points in light red)||19 points|
|11 points (non-cross-type in light red)||Inner 9 points|
|Outer 9 points|
As with the 1D Mark III you can use the two control dials to select AF points (once you've pressed the AF selection button). Turning the main dial moves the AF point laterally across the frame, while the rear dial selects the AF point above or below the current one, rotating about the central point. This very quickly becomes second-nature, if it's not already familiar from the 1D Mark III, making it easy to select AF points without removing the camera from your eye.
The camera doesn't limit you to this one way of working, however, and you can also use the joystick to move directly to your preferred point. And, like the recently-introduced 7D, you can define different default AF points for the three orientations you might shoot with the camera (landscape, portrait with grip up and portrait with grip down).
In One-Shot AF mode the camera is simple to use and it's easy to select the point you wish to use. There's an AF microadjust option if you wish to fine-tune the focusing behavior of any of your lenses.
Although an autofocus system this involved and customizable will inevitably become quite complicated to fine-tune, there are several aspects that make configuring it more complex than necessary. In terms of its use as a sports camera, there are nineteen custom functions in the AF/Drive group. Three of these deal with the behavior of AF-tracking, but oddly they are spread across custom functions C.Fn III-2, 4 and 8, rather than being clustered together.
C.Fn III 8 dictates how many AF points are used by the camera - the chosen point, the chosen point plus the two points on either side of it, the chosen points plus all neighboring points or all 45 AF points. C.Fn III 4 defines whether the camera gives priority to the subject or the user-chosen AF point, while C.Fn III 2 determines how long the AF-tracking will wait before attempting to re-focus if the subject is lost or something obscures the subject.
Once AF-tracking is engaged, C.Fn III-2 defines how long it will try to remain on the subject before trying to refocus, if the subject appears to have been obscured. However, if C.Fn III 4 is set to give priority to the AF point, this will overrule C.Fn III 2 and re-focus as soon as anything new passes into the AF point. C.Fn III-2 also dictates the speed the camera will try to refocus when working with a single AF point.
To our minds it would seem more logical for custom functions 2 and 4 to be combined (since they interact and can overrule each other), and possibly be made into a sub-option of an over-arching 'AF tracking' function. Indeed, overall, it would appear more sensible to have a single options page to define its precise behavior.
The only logical reason for using such a confusing structure would appear to be the hope of providing continuity with the previous cameras. This unwillingness to change is understandable, given it’s likely that at least some of the problems with the AF system on the 1D III are likely have been caused by users not initially understanding its added complexity, but the result is a system of fine-tuning that is unnecessarily complex.