Focus points: A single focusing point
Early EOS cameras have just one, central, focusing point. It is an effective system that emulates the centrally-positioned focusing aids of the previous generation of Canon’s manual focus FD SLR cameras. With a single, central focusing point, the lens focuses on whatever the focusing point is covering. This works fine – as long as you want the part of the scene that’s in the centre of the frame to be in focus.
If you don’t, you can use focus lock, but that takes time and also means that you have to think about what the camera is doing. Not ideal for an autofocus system. So Canon introduced multipoint focusing. It first appeared on the EOS 10 in 1990; today, it’s standard across the range of EOS cameras and it’s hard to imagine using a single-lens reflex camera without it.
For many of your photographs, there’s a fair chance that you’d get by with a single, central focusing point. After all, the main subject – the thing you want to be in focus – will often be in the centre.
A typical problem with a single, central focusing point occurs if you are photographing two people standing close to each other. The camera will focus on the background in-between your subjects, who will then be out of focus.
If you have two people in the frame at different distances from the camera, a central focusing point may bring one person into focus, but will it give the result you want?
You might want to position the subject to one side of the frame. With single-point focusing systems, however, when you place your subject to one side the camera still uses the central point to focus, and you run the risk of the main subject being out of focus.
Multipoint focusing lets you place the main subject wherever you like in the frame, and it will still be in sharp focus. Most EOS cameras will either automatically select a focus point for you, or let you step in and make the selection yourself.