ARTICLES - CRAFT & TECHNIQUES
By: Trent Duncan, Instructor
Choosing the right lens is essential for filmmakers when visually telling a story. In order to understand the benefits and limitations of lenses, you first need to understand Focal Length.
WHAT IS FOCAL LENGTH?
The Focal length of a lens is an important aspect of filmmaking because it determines the field of view in your frame. Focal length also helps to compress or separate elements within your shot. The standard measurement for focal length is measured in millimeters, regardless of whether you’re shooting with a zoom or prime lens. Simply put, the technical definition of focal length is the distance, in millimeters, from the camera’s image sensor to the center of the lens. This also explains why a lens with a focal length of 20mm is physically shorter than a lens with a focal length of 250mm.
HOW DOES THE FOCAL LENGTH AFFECT YOUR IMAGE?
When looking through the viewfinder of your camera, a smaller lens size will widen your field of view while a larger lens size will narrow your field of view. The lower the focal length, the more your view becomes wider and distorted, resembling a “fish eye” look. Increasing the focal length of a lens will do the exact opposite. A lens with a higher focal length will begin to crop your shot and “zoom” closer toward your subject. By changing lenses from a 35mm to a 150mm, you are effectively increasing the focal length between the lens and the camera’s sensor, which is creating a zoom effect, narrowing your field of view and bringing your frame closer to the subject.
HOW DO DIFFERENT FOCAL LENGTHS COMPRESS OR SEPARATE ELEMENTS IN YOUR SHOT?
By changing the focal length of your lens, you’ll be able to manipulate the elements in your shot to achieve different cinematic looks. When using a lens with a small focal length (35mm or less), your shot will be wider, this will add separation and distance to the elements in the background. In essence, they will seem smaller and farther away. At the same time, the elements closer to your lens will appear larger and more dominant in frame. When using a lens with a large focal length (50mm or more), it will compress the elements in your shot, making the distance between each element appear closer to one another. This may not seem favorable, but generally, larger focal length lenses will create a shallower depth of field. This makes those elements in the background that are appearing closer, out of focus. The depth of field achieved by a large focal length lens is what many filmmakers refer to as “creating a cinematic look”.
With a variety of lenses to choose from, filmmakers have many ways to tell their story. The good filmmakers, however, will manipulate their lenses to influence the image in order to better tell their story. The more you know, the better filmmaker you’ll be.