Focus lock

Cameras with just a single central focusing point might appear to be limiting. After all, you don’t always want your subject to be in the centre of the frame. But these single sensor cameras are actually very versatile.

To focus on an off-centre subject, simply move the camera, positioning the centre of the viewfinder frame over the centre of the subject. Now partially press the shutter button. This will lock the focus without taking a picture. Keep the button partially pressed and move the camera to recompose the viewfinder image. Increase the pressure on the shutter button to take the picture.

Focus lock also locks the exposure. If you want to take focus and exposure readings from different areas, first compose the image in the viewfinder so that the area you want to take an exposure reading from is in the centre of the frame. Then press the exposure lock (*) button on the back of the camera. Next, recompose the image and press the shutter button. This will refocus the lens and take the picture, while using the locked exposure.

Registered AF point

A new feature found on some recent digital cameras is the Registered AF Point (which is also known as the Home Position). This allows you to pre-select a focus point and switch to it instantly whenever required.

On the EOS-1D and 1Ds series, you first select the AF point normally and then register it by pressing the Assist and FEL buttons.

During shooting you can return to this AF point at any time by pressing the Assist and AF point selection buttons together. Alternatively, by setting C.Fn.-18-1 on the EOS-1D or 1Ds models, you can switch to the registered AF point just by pressing the Assist button.

This feature is probably most useful for sports photographers, who may have two or three areas of the viewfinder where the action is most likely to take place. However, remembering to switch focus points at the right moment will need some practice.

If your camera does not offer a Registered AF point, switch to the centre point instead, and use focus lock to keep your chosen subject sharp.

Using multiple sensors

The camera can only use data from a single AF sensor to focus. When there is more than one focus point a selection has to be made. This can be done automatically or manually.