Here is a quick excerpt from his article:

It’s worth noting one other fundamental difference between the AF system in the D3S and that of the EOS-1D Mark IV. When Nikon focus is out, it doesn’t tend to be way out. More often than not, peak action frames that are not perfectly focused aren’t that blurry, making some of them still viable. That is, if you’re of a mind that it’s better to have a slightly soft frame of a great peak moment than a totally blurry one. The EOS-1D Mark IV, on the other hand, produces many more frames that are too soft to use for anything, no matter how sweet the moment.

To sum up, our experience with the D3S’ AF system is that it’s trustworthy and dependable enough for us to be confident using it for peak action sports. Not perfect: it needs to be a bit faster off the line, in addition to the other quibbles we’ve mentioned. But it does work as needed most of the time, which is in stark contrast to the experience of the EOS-1D Mark IV in the last month.

The above review is pretty much in line with what many other sports and action photographers have said after doing comparisons between the two cameras – the Nikon D3s is currently, without a doubt, a leader in both autofocus and low-light photography (high ISO performance).

When I looked at some sample pictures of the Canon EOS 1D Mark IV, I got a little worried about Nikon D3s future. However, after seeing some high ISO comparisons and hearing from pros on autofocus performance of both cameras, it turned out that D3s is the leader and it looks like it will stay that way for at least another two years! Sure, it is unfair to compare Nikon’s full frame sensor with a 1.3x cropped sensor, but poor autofocus performance has been Canon’s biggest weakness (especially in 1D Mark III) and despite the fact that Canon re-engineered their autofocus system from scratch in 1D Mark IV, it is still worse than Nikon’s legendary 51 point autofocus system.

Nikon D3s wins, end of story.

Canon EOS 1D Mark IV

Here are some of the key highlights and differences between Canon EOS-1D Mark IV and Nikon D3s:

1. A brand new 45 point auto focus system (Nikon D3s has 51 focus points).
2. Fast 10 frames per second operation (Nikon D3s is 9 FPS).
3. Default ISO range of 100-12800 with “boost” modes up to ISO 102400 (Nikon D3s is 200-12800 & also up to ISO 102400).
4. Full HD 1080p video recording capability (Nikon D3s is only 720p).
5. Canon EOS-1D Mark IV features a 16.1 megapixel CMOS sensor (Nikon D3s has a 12.1 mp CMOS sensor).
6. A large buffer that can handle up to 121 large JPEG images (Nikon D3s can handle 130 JPEGs @ 12.1 mp).
7. Both Canon EOS-1D Mark IV and Nikon D3s have the same 3″ size screens with 920,000 pixels.
8. The sensor on Canon EOS-1D Mark IV has a 1.3x crop factor (not full frame), whereas the Nikon D3s sports a full frame sensor (FX).
9. Canon EOS-1D Mark IV is priced at $4,999.00, while Nikon D3s is priced at $5,199.95.

Just looking at the above specs, this camera beats the Nikon D3s in some categories (although the most important ones are auto focus, sensor size and noise in high ISOs, where Nikon seems to have the lead). The 1D Mark IV beats the D3s in price, but not by a big margin. Image quality at high ISOs seems to be very good and I would say very comparable to Nikon D3s – here are some samples for you to take a look at. Considering that the sensor has more pixels (16.1 mp vs 12.1), Canon has done a remarkable job in sensor development.

At the same time, the Nikon D3s has a better battery life, weather sealing and build quality compared to Canon 1D Mark IV. The controls on the Nikon bodies are always more intuitive and better designed compared to Canon, which is also a big deal, at least for me. So, it is definitely not fair to say that Canon has a big lead over Nikon. Specs look good, but only a real head-to-head test comparing image quality, auto focus and other features will truly reveal who the winner is. At the end of the day, does it really matter? If you own Canon gear, you will want the 1D Mark IV, whereas Nikon shooters will choose the Nikon D3s. For those who want to switch from one brand to another, I would suggest to carefully re-evaluate your needs and see if it is truly worth it.

It would be interesting to see how good the new 45 point auto focus system is compared to the legendary Nikon 51 focus point system. If they have a comparable or better auto focus system, Nikon will probably lose some of its market share to those who are purely looking at hard specs. Although I can understand the technical challenges of not being able to shoot HD video with the current Expeed processor, Nikon made a mistake by providing a mediocre 720p video recording in the D3s. Afterall, the D3s is supposed to be the “top of the line” camera for news and sports photographers and putting 720p into it doesn’t necessarily make Nikon look good in front of true professionals. If you are giving a feature in the best camera, give the best features, I would say.

Update: Rob Galbraith posted a detailed review of Canon EOS-1D Mark IV’s autofocus performance and his conclusion is that Nikon D3s has better autofocus performance. Here are my observation notes on Canon EOS-1D Mark IV autofocus vs Nikon D3s.