Sports shots are pretty intolerant of incorrect focus.
The focus software built into your camera does its best to give you crisp focus in all conditions, but since all it knows is what you’re pointing it at, it has to make some guesses and some compromises. There are a couple of things that you can do to give it more information so that it can make better decisions and improve the number of in-focus shots. You’ll notice the common thread in this post – rather than let the camera make choices for you, you are making the choices yourself.
Focus mode
There are two basic types of subjects – those that are static, and those that are moving. In the default mode (AI Focus on Canon, AF-A on Nikon), the camera looks at the subject and tries to figure out which autofocus approach works better.
My experience on the cameras I’ve used (Canon XT & 40D) is that the camera often makes the wrong choice. You can get better results by choosing the focus mode optimized for moving subjects (AI Servo or AF-C).
Focus points
Your camera has an array of focus points – individual spots in the scene where the camera can detect focus. The number and sophistication of those focus points depends on the model of the camera – my 40D has 9 focus points, and the new 7D that I’m pining for has 19 focus points.
Like the focus mode, the camera looks at all the focus points and tries to determine which ones are most important and then focuses on those. Sometimes it works well, sometimes you find that in that beautifully-composed and exposed image, the camera decided it was better to make sure the fan in the background be in focus than the players.
Like focus mode, you can help the camera out by telling it what you think is important. By setting on focus point, you know if you put that focus point on the part of the image that you want to be in focus, the camera will try to put it in focus. Say you’re shooting runners and you want their faces in focus, you choose a focus point at the top of the frame.
However, all focus points are not created equal. On my 40D, the center focus point is better – it will work for lenses with higher minimum apertures than the other ones, and it may give better results as well.
When I’m shooting most sports, I stick with the center focus point because I know it will work well and I’d rather give up a little framing and have to crop an image down rather than try to shift the focus point from shot to shot.
Focus-on-demand
The camera chooses when it wants to focus, which can be inconvenient. You want to focus on the face of a player in a static situation and take the picture when the motion starts, but when you take the picture, the camera refocuses to what the focus point is on.
If your camera supports focus-on-demand, you can turn off the focus when you half-press the shutter and map the “focus now†function to a button on the back of the camera, which you press with your thumb. You now get full control on the focus, and on my 40D, the chosen focus point lights up red when the camera detects focus.
Enabling this is not without a downside. First, instead of just following the action, keeping the focus point where you want it, and pressing the shutter-release when it makes sense to take a picture, you also need to press the focus button (and sometimes hold it) at the appropriate point. For me, it took 4 games before I was approaching parity with the performance I was getting with the camera controlling focus, and a few more before I saw any benefits. And you run the risk of forgetting to press the focus button in other situations, like when you are taking a wonderfully wind-blown team photograph in perfect light. Not that I’ve ever done that.
I have this set all the time on aperture-priority on my camera. It’s possible to set it up on one of the custom modes on my camera – so it only does that when you turn the mode dial to C1 – but the power-off/on behavior in that mode resets the ISO so it doesn’t work for me.
It was a fair bit of pain to learn to do this but it’s made a noticeable difference in the quality of my images.
Release priority
One more small point about focus.
Canon cameras in AI servo mode operate in what is known as “release focus†for the first frame in a sequence. That means that the camera doesn’t delay taking the picture even if the camera hasn’t achieved focus. Later frames are “focus priorityâ€, which means the camera knows when it’s going to take the picture and tries to have focus at that point.
So, even if you aren’t going to change the focus point or use focus-on-demand, it helps a lot of you stake sequences of shots rather than single shots – the later shots are more likely to be good.
Micro adjustment
Guess I wasn’t quite done.
The auto-focus system works through the collaboration of the camera and the lens. The camera detects the focus and drives the lens to perfect focus.
Well, it’s not quite that simple. Cameras and lenses are both physical devices and manufacturing tolerances mean that some of them focus really well, while other will back focus (the true focus point is actually behind the subject) or front focus (the true focus point is behind the subject). It’s the luck of the draw.
If you do focus tests – which I might talk about at some point, until then you can search the interwebs – you can tell how your camera/lens perform, and then send the lens and/or the camera (they work together) off to your manufacturer for calibration.
Or… you can buy a camera body that supports micro adjustment. You test the focus, and then you can dial in a little adjustment to get things just the way you want it. Another reason I’m pining for the 7D.
So, what do you think ?