Published on 27 June 2022 5 min read

What is the focal length of a lens? Focal length is the term we use to define the distance, in millimeters, between the optical center of the lens and the camera's sensor. It is found with the camera focused on infinity. We know that photography is the art and practice of creating images by capturing light. The focal length of your lens is a major component in this practice. When light enters the front of a lens, it bends into a single point of focus. This is the optical center. The greater the focal length is, the closer the image appears, and the smaller the focal length, the further the image appears.

What Focal Length Means in Practice

Focal length is almost always going to be the first thing a photographer considers when choosing a lens and setting up for a shoot. The focal length of the lens used determines how the subject appears in relation to the rest of the photograph.

For example, a short focal length lens is typically used for landscape or real estate photography because it will produce a photograph with a wide angle of view. 12-16mm are often used in real estate photography because these wide-angle lenses create a photo in which the subjects appear smaller, capturing more of a room in a single shot. Short focal lengths can also be used for taking pictures of large groups or documenting small spaces.

It is important to note that very short focal lengths, especially those with very wide angles, can distort your image. The edges of the frame will appear warped or bent. An example of a dramatic wide angle would be what is known as a fish-eye lens. These lenses can be great for dramatic and artistic effects, but perhaps not the best choice for taking portraits or headshots.

On the other hand, focal lengths of 60mm or more, known as telephoto lenses, can have the opposite effect. When using a very long focal length, or zoom lens, you may notice not so much a distortion as a compression of your subject. These lenses are ideal for taking photos of subjects very far away, such as sporting events or wildlife.

How to Determine the Focal Length of Your Lens

As mentioned before, the focal length of your lens is measured in millimeters. Luckily, lenses are usually very clearly labeled by their focal length, so no careful measurements on your end are typically required. Conveniently, lenses are named by their focal length. If you are unsure of the focal length of your lens, you can find this information on the barrel of the lens. It will be a number of millimeters, most commonly somewhere between 14mm (this would be your wide-angle lens) and 135mm (this would be a zoom lens).

Why Focal Length Matters

It is vital that a photographer understand the practical effects that the focal length of their camera will have on the outcome of their photos. The angle of view, which is how much of the scene is captured in the image, is affected by the focal length. A wide angle, or shorter focal length, will capture more of the surrounding view. A longer focal length will give a much more narrow view and result in a tighter shot.

The apparent size of the subject is affected as well by the focal length in that longer focal lengths will compress distance. This makes it appear as if the foreground, middle, and background are closer together. Shorter focal lengths will have the opposite effect and increase the appearance of distance between these planes.

Common Lenses by Focal Length (and How to Use Them)

14-35mm lenses are considered wide-angle. These lenses are best used for landscape and architectural photography. These are commonly used in real estate photography as they can capture many details, even in a small space. There are lenses that are even wider, found anywhere from 4mm to 14mm, and these are considered super wide-angle, or fish-eye, lenses. These create a heavily distorted image and are great for abstract or artistic shots.

Anywhere from 35mm to 85mm is considered a standard lens. These are the lenses most commonly used by photojournalists for street or “slice-of-life” photography. A 50mm lens is considered a standard go-to lens that can be used successfully in many different situations and is best for portrait work.

Lenses that are 85mm or longer are considered telephoto or zoom lenses. These are best for action shots, such as sporting events. These lenses are also used for capturing close-up images of subjects very far away, such as wildlife. Extreme zoom lenses, which can be 2,000mm+, are used in astrophotography to capture galaxies and nebulas lightyears away.

Implementing Your New Understanding of Focal Length

With your new understanding of how focal length is used in photography, you can now research and purchase lenses with varying focal lengths to suit your specific photographic needs. Are you taking professional headshots for someone? Remember that for portrait-style photography, a focal length of around 50mm is going to look best. This can help keep the subject of your photo crisp and clear while creating a creamy, subtly out-of-focus background that makes portraits pop.

If you are taking photos of landscapes or cityscapes, you know that you probably want a wider angle lens in the range of 14-35mm. This focal range will keep all of the important details in focus and help you capture as much of your subject in frame as possible. When looking for a new lens, it is also important to remember that some lenses are designed for specific camera bodies, so always double-check that the lens you are interested in will actually work with your camera before making a purchase.

In summary, we now know that:

Camera focal length refers to the distance, in millimeters, between the optical center of the lens and the camera's sensor.
The focal length can tell us how much of the scene will be captured in the image and how much of that scene will be acceptably sharp.
Understanding focal length is tantamount to taking quality photos.
As a general rule, the smaller the focal length number, the wider the angle, and the larger the number, the greater the zoom.

Now that you are armed with your newfound expertise on focal lengths, get out there and start experimenting with different lenses. Consider taking a photography class to hone in on various photographic styles and modalities.