Pre-focus for perfection?
QI have a chance to shoot motorsport trackside. Can I pre-focus for action images to get them sharp enough, as I’m not sure my reactions are quick enough to focus on the subject itself?
APre-focusing is a good option when it comes to action, but it depends on how predictable the movement of your subject is. For example, pre-focusing for wildlife is difficult, as you rarely have a situation where you can be certain where an erratically moving animal or bird is going to be. It’s the same with sports such as football and rugby; you know the players are on the pitch, but you can’t be certain which way they are going to run.
If your subject’s line of movement is more regular, then pre-focusing is a technique to try. You can autofocus on the track at a point you know the car will pass, then lock that focus off by switching to manual. It’s useful to have a marker on the track – like a chevron – that you can use as a guide to when to press the shutter button, and it is important not to move position. It’s also a good idea to give yourself room for error by choosing an f/stop such as f/8 so you have greater depth of field in case the subject doesn’t pass exactly where you expect it to. You also need to make sure your camera’s drive mode is on its highest continuous shooting speed so you can take a burst of shots as the subject passes in the hope that at least one will be perfectly sharp.
Lastly, set a very fast shutter speed, otherwise it won’t make a difference if you’ve pre-focused in the right spot; your subject will be blurred. I suggest a minimum of 1/2000 sec to be sure of a sharp shot.