THE MAIN FOCUS

While the 1D Mark IV has been touted as having a completely rebuilt autofocus system, that's not exactly true. What the Mark IV has is basically the same 45-point AF system as its predecessor but with 39 extra-sensitive cross-type points rather than 19 cross points as on the Mark III. (In contrast, the 12.1MP Nikon D3s uses a 51-point AF system with 15 cross-type sensors.) Though there's real tech behind these specs, some of it is just PR puffery. The important thing is, of course, whether it works.

Soon after receiving my Mark IV test unit, Canon released a firmware (1.0.6) update for the camera which was designed to enhance AF performance "for receding subjects and for subjects that are approaching at a low speed." Not a good sign considering how much hand wringing had gone on before the Mark IV came out.

Most complaints about the Mark III's AF system came from photographers who shot with the camera on unusually hot and humid days; the Mark IV didn't start shipping until the winter in early 2010. (Conspiracy theories anyone?)

I photographed mostly indoor sports because I wanted to test the camera's expanded high ISO shooting capabilities. Yes, in addition to the revamped AF and HD shooting capability, the other headline about the Mark IV is its broader ISO range: ISO 100-12,800 in standard mode along with a specialty low setting of ISO 50; and boosted high ISOs of 25,600 (H1), 51,200 (H2) and 102,400 (H3).

But first, the autofocus. I purposely set out to test the camera in high-action shooting conditions with dim, low contrast lighting which is the bugaboo of most AF systems. First I photographed an amateur basketball league with the old gym's flickering lights looking downright sickly. Though it was hard to avoid that ugly yellow cast in my RAW image—fixable later in Adobe Camera RAW/Photoshop—the Mark IV's AF was spot on. I shot using the manually selectable center point focus along with letting the camera automatically select the focus from the 45-point array. I mainly used the new AI Servo II mode—which has a new focusing algorithm—but also tried One Shot for static images or if I could predict where the action was going to end up.

Perhaps the "special sauce" is in the new AI Servo II mode, but I got great results shooting with the Mark IV and a Canon 70-200mm f/4L IS USM lens. The only softness I saw was from Chroma noise at ISO 6400 which I needed to maintain a fast shutter speed because of the poor lighting conditions. (More about image noise later.)

Next I shot an indoor soccer game in a hazy sports complex and the AF/AI Servo II once again did a good job tracking the action and producing mainly (65-75 percent) sharp images. The plastic screens around the indoor field provided a bit of a challenge but I was able to work around the obstructions and even when shooting through them, the Mark IV's AF did surprisingly well. (Again, most of the softness came from noise at the higher ISOs.)

Finally, I shot a college hockey game—New York University vs. the University of Pennsylvania—in a fluorescent-lit rink. The hockey match posed perhaps the greatest challenge for the AF since the players were moving at a high rate of speed and the reflection of the ice contrasted sharply with the dark jerseys of the visiting team and the bright white and purple of the NYU players.

Though the ten frames per second shooting speed of the camera was almost faster than the flicker of the fluorescents causing some unusual (read: ugly) lighting in my shots, the Mark IV's AF was fast, reliable and, quite often, tack sharp.

I'd love to see how the camera performs in hot and humid conditions but I guess I'll leave that to photographers in warmer climates to test out.