Camcorder Controls: Understanding Focus Pulling
Focus pulling seems like it should be a simple thing to do. In actuality, this job is one of the most difficult to master. It takes a lot of practice and experience to become a strong focus puller who can ensure that every moment of a given film will be in focus.
Step 1: Examine a Lens
Take a look at any lens and find the focus ring. The ring should have a series of numbers around it. These correspond to the distance from the focus plane to the subject. Some lenses will have two sets of numbers: one for meters and another for feet. Meters are almost always in white while feet are colored. Now, you must find the focus plane. It will not be anywhere on the lens, but on the camera at the point where the image hits the film plane or digital chip. Since this is inside the camera, you cannot see it, but the appropriate spot to measure from is indicated by a little circle with a vertical line going through it.
Step 2: Why not Focus by Eye?
The question may have already come to mind, why does it matter how far the person is from the camera if I can see whether or not they are in focus in the viewfinder? Well for one, viewfinders are very small and do not always display the most critical of focus conditions. Secondly, if a person is walking towards the camera, you will not be able to pull the focus with them strictly by looking at the image. So, you need to watch their distance from the camera and rotate the focus ring to correspond to how far away they are.
Step 3: Measuring
Now you need to determine how far the person is from the camera. You can do this by focusing by eye and then marking the spot on the lens. But again, viewfinders are not always accurate. So, measure the distance from the camera to the person's start point. Do the same for their end point. Now you should also take some intermediate marks so that you can keep them in focus throughout their movement. Place tape marks on the floor at each corresponding spot so you can keep track of the distances.
Step 4: Pulling
Keeping the person in focus will not be as simple as hitting each mark at the same time as they do. You will need to gracefully and fluidly stay with them even between the marks. You may have noticed that as the person gets closer, the distance between the marks on your focus ring increases, even as the distance they cover stays the same. So, you will need to increase the speed of your rotation to account for this. Note also that as the person gets closer, the focus becomes more critical.
Pulling focus is not merely a matter of turning a knob. But with practice, you will end up considering all these factors second nature.