With [One-Shot AF], while you press the shutter button halfway to focus a still subject, the focus will be locked. You can then recompose the shot and press the shutter button completely to take the picture. This is called "focus lock".
It is an effective method for shooting scenes with both close and distant subjects, such as animals in a cage and people in front of a landscape.

Example of Focus Lock

In normal autofocus settings, if you want to take a picture by focusing on the nearest flower, the focus is usually on the leaves at the center as shown in the left picture.
In such cases, use Focus Lock to focus on the target subject as shown in the right picture.

Shooting with Focus Lock

1. Set the power switch to <ON>.

2. Set the lens focus mode switch to <AF>.

3. Press the <AF>(AF mode selection) button.

4. Press the <Cross Keys> to set the AF mode to [ONE SHOT] (One Shot AF), then press <SET> button.

5. Press the shutter button halfway to autofocus.

When focus is achieved, the AF point which achieved focus will be displayed, and the focus confirmation light [ ] in the viewfinder will also light.

6. Recompose the picture, while pressing and holding the shutter button halfway down.

7. Press the shutter button completely to take the picture.

• EOS 1100D