One of the worst feelings as a filmmaker is to spend hours getting a shot just right, only to discover that it was out of focus. Having sharp focus is absolutely quintessential, and draws the line between seasoned and beginner filmmakers. There are several factors that affect focus, and we’re here to help you understand them, so you can get the sharpest image possible.
Before we even talk about the factors, what exactly is depth of field? Essentially, depth of field is a measurement of the range of acceptable focus in a frame. So if your depth of field is 9m, anything outside of that 9m will be out of focus. The placement of this range is based on the 1⁄3 - 2⁄3 rule. This rule states that if you focus on a subject, 1⁄3 of the depth of field will be in front of the subject, with the other 2⁄3 behind. So going back to the 9m, if you were to focus on a subject, 3m in front of them would be in focus, and another 6m behind them would also be in focus. Now that you know what depth of field is, we can talk about the 3 factors that affect them.
#1 - Aperture. The aperture of a camera is how open the lens of the camera is, and so how much light can be registered. When a camera’s aperture is more open, the depth of focus will be less, or more shallow. If the aperture is more closed, the depth of focus will be higher, or deeper.
#2 - Lens / Focal Length. Different types of lenses have huge effects on the image a camera produces. The wider a lens is, or the lower the focal length, the deeper the depth of focus will be. The longer the lens, such as telephoto lenses, the deeper the depth of field.
#3 - Distance of Subject to Camera. If you focus on a subject, the distance of them to the camera affects the depth of field. The closer your subject is, the shallower the depth of field. The farther they are, the deeper the depth of field.
