The AF of a Canon 40D Leaves Much to be Desired

Call me lazy or call me clumsy if you want, but auto focus has become extremely important for me. I have to concentrate on so many things when I photograph, that I don’t want to have to worry about AF too. But dang it, I’m tired of things like these:

At first glance these photos might look impressive, but click on them and you’ll see that the focus is wrong! I have hundreds of examples like these: sometimes the focus is too near, sometimes too far, with the same lens or with different lenses.

You want more examples? Look here. All these are taken with decent stage lighting and the 40D hunts and hunts for focus. I have to half-press the shutter 3–4 times and if I’m lucky, it would manage to focus somewhere. I usually have no more than 5–10% of decently focused shots taken at a concert.

So let’s not beat about the bush: the AF on my Canon 10D was mediocre, on the 30D only slightly better, on my current 40D it’s unchanged, so it remains mediocre. What I mean is, it’s OK in daylight with wide-angles and normal lenses, and it’s OK with a teles for non-critical applications, but altogether I’m tired of throwing away good shots because the camera is not doing its job.

You might think I need to learn how to focus well, but this is definitely not the problem. Long ago I started using the central AF point only and I do the focus-on-the-eye-then-recompose-and-fire technique every time. I never shoot continuously and I do take the time to compose, focus and recompose each shot. And I’ve been having the feeling that all the middle-class Canons are mediocre at best when it comes to AF precision.

The New Canons

In the 5D2 white paper Canon says that its sensor “achieves the highest performance of any sensor in the Canon DSLR lineup”. Now that’s a significant claim, and I’m even willing to believe it.  In fact, I’ve been tempted by that camera ever since it was announced. But there is the AF uncertainty. Here is what Canon says in that same white paper: “The AF systems on both the EOS 50D and EOS 5D Mark II are very similar to the systems on the models they replace”. So the 5D2 has a very similar AF system to the 5D (mark I) which was only slightly better than that of a 30D, which I had and which was decent, but with all weaknesses that I’ve notice and mentioned here. And the 50D has a very similar AF system to the 40D, which I have and which is not good enough. So let me ask you this. What good is a camera with superb low-light qualities if the AF cannot keep up?

And what about the Canon 7D? Many claim that it has the best AF of all Canon bodies of all times, but unfortunately I couldn’t find an official reference for this claim. A few months ago I was in a camera store and briefly compared a 7D and a 5D2, and the 7D was indeed quicker and “surer.” By this I mean no hunting, no readjustment if you half-press the shutter a second time, etc.

The Nikons

I shot with a Nikon 300D about a year ago and was extremely impressed with its AF. It was at night: 5 people playing Wii and being illuminated only by the light of a television set. The AF of the 300D was fast and absolutely reliable, the shots were indeed very good.

The other day I borrowed a Nikon D90 from a friend, and this camera too has very impressive AF.

The Shootout

So I did a test. The borrowed Nikon D90 with a 35/1.8 and 70-300/4-5.6 versus a friend’s Canon 7D with 50/1.8 II and 70-200/4 IS versus my Canon 40D, 50/1.8 and 70-200/4. I compared the cameras indoors, focusing on different things in my apartment and turning the lights progressively lower until the AF gave up. The 40D focused well at decent light levels on things with high contrast. Trying it out on wrinkled bed-covers and other things with less contrast threw the AF off more than once. Often half-pressing the shutter, then half-pressing it again would cause a slight refocusing. Not much, but since the camera did not move in any way, the focus should not change either.  As it is, at least one of the shots will have inaccurate focus.

The 7D and D90 showed no weaknesses at this point whatsoever, and I turned the lights further down.  The 40D started having more and more problems, the 7D and D90 were still going strong. At the point where a person would have difficulty reading medium-sized printed text, the AF of the 40D gave up completely. It would just focus from infinity to the closest focus point and back, but would never lock focus. Not even with the 50/1.8 lens. The 7D and D90 were slower that before, but still very impressive. Having such AF performance at a concert would be absolutely enough for me.

To find the limits of the 7D and D90 I dimmed the light to something like candle-light brightness and started focusing further and further away from the light. And what do you know?  In terms of AF performance (speed and accuracy with stationary objects) the mid-class Nikon D90 was on par with the Canon 7D, the camera whose AF is rumored to be the best of all Canons. While I am very happy that it’s possible to get a mid-priced camera with a superb AF system, I am also quite surprised by how incredibly good the Nikon D90 is. OK, it has less pixels and a slightly smaller viewfinder than the 7D, but it costs exactly half of what a 7D costs, and it’s smaller and lighter and I do not want more than 12 MP anyway. The D90 has a much nicer viewfinder than the 40D, by the way…

Decisions, Decisions

OK, so what am I going to do? I don’t know quite yet, but I know this: I’m not going to make another important trip with a Canon 40D, and I’m not going to buy a Canon 5D2. I might:

  • get a Canon 7D, but I find it overpriced and I want a full-frame camera,
  • wait for the 5D mark III, but this could be a very long wait,
  • switch to a Nikon D90, but I’m not impressed with Nikon’s DX lens offerings.  Why doesn’t Nikon have any high-quality f/4 DX lenses?!
  • or I might get a Nikon D700, but it’s so huge and the good lenses (14-24, 24-70, 70-200) are also huge and expensive, and I’m not a professional, and I’m not willing to carry all that weight.  Why doesn’t Nikon have any high-quality f/4 FX lenses?!

So, no obvious alternative at this moment, but I’ll look at the Tamron and Tokina offerings for Nikon DX, and if I find something decent, the winner might just be a Nikon D90. That would mean I’d have to change systems, and that wouldn’t make me one bit happy…