Focal Length

What is Focal Length?

In photography, focal length is a term that represents the distance between the lens and the image sensor when the subject is in focus, measured in millimeters. It is a fixed characteristic of the lens when it is set to ‘infinity focus’. It is not a measurement of the actual length of a lens, but it is a calculation of the optical distance from the point where light rays converge to form a sharp image of an object to the digital sensor in the camera. The term “focal length” can apply not only to traditional photography but also to any system that uses lenses like telescopes, binoculars, microscopes, and even the human eye. In all these cases, the lens (or lenses) and the focal length work together to focus light and form an image. Specifically, in traditional photography, focal length is responsible for two primary attributes – magnification and angle of view. Magnification indicates how large the subject appears in the final image, while the angle of view determines how much of the scene will be captured in the image. 

How does Focal Length work?

A lens with a short focal length (18mm or 24mm), known as a wide-angle lens, has a broader field of view, capturing more of the scene in the frame. It tends to magnify the perception of distance between objects, making them seem further apart than they actually are. These lenses are typically used in landscape, architecture, and interior photography where the goal is to fit as much as possible into the frame. A telephoto lens is a lens with a long focal length (200mm or 400mm) that has a narrow field of view and higher magnification. These lenses appear to compress distance, making objects seem closer together than they actually are. This makes them ideal for wildlife, sports, and portrait photography where the aim is to magnify distant subjects or achieve a shallow depth of field.  Longer focal lengths provide the “bokeh” effect in photography which focuses tightly on the subject while blurring the background and foreground.

Why is it important to understand Focal Length?

In terms of technology, understanding and applying the concept of focal length is pivotal to crafting different kinds of images and visual effects. It is not only crucial to photography, but also in fields like cinematography, astronomy (with telescopes), and even in the design and use of corrective eyewear. For photographers, lens selection in terms of focal length is a key consideration in influencing the final visual output and storytelling of an image. With the advancement of technology, some cameras and smartphones allow for adjustments of the effective focal length digitally, either by cropping the image (digital zoom) or by combining the information from multiple lenses. 

Scroll to Top