Published: March 12, 2025 | Last Updated: May 21, 2025
What is focal length? Definition & Meaning
Focal length is measured in millimeters and determines the optical distance between the lens’s center and the camera’s sensor. More importantly, it defines how much of a scene is captured and how it looks, whether it’s a sweeping wide shot or a tightly focused close-up.
When you hear someone suggest a “wider lens,” they’re talking about lenses with shorter focal lengths, like a 24mm or 35mm. These lenses capture more of the environment, making them ideal for establishing shots or scenes where the setting plays a major role.
Think of The Revenant (2015, 20th Century Fox), where Emmanuel Lubezki used ultra-wide lenses to pull viewers into the harsh wilderness alongside Leonardo DiCaprio. The lens choice made the viewer feel the biting cold and vast isolation.
Telephoto lenses, like 85mm or above, are on the other end of the spectrum. These narrow the field of view, isolating your subject and blurring out distractions.
Depth of Field: More Than Just Focal Length
While focal length influences depth of field (DOF), it’s not the only factor. Depth of field is primarily controlled by three elements: aperture size, distance from the subject, and focal length.
Aperture
A wider aperture (like f/1.8 or f/2.8) creates a shallow depth of field, making the background appear blurred. A smaller aperture (like f/11 or f/16) increases the depth of field, keeping more of the image sharp. This applies to both wide and telephoto lenses.
Distance from the Subject: Getting Closer Narrows the Focus
The closer the camera is to the subject, the shallower the depth of field becomes. Even with a wide-angle lens, the background can blur if you’re right up close. Conversely, a telephoto lens shot from a distance will have a deeper focus.
Focal Length: Enhancing Perceived Blur
Telephoto lenses (like 85mm or 100mm) naturally compress space, making the background look closer and more blurred, even at the same aperture as a wide lens.
Wide-angle lenses (like 24mm) usually keep more of the scene in focus, but they also exaggerate distance between objects, which can minimize blur when compared to a telephoto lens shot from the same spot. How much is in focus at a given sensor size and aperture depends on the lens’s hyperfocal distance.
Practical Example:
- Shooting a portrait at f/2.8 with an 85mm lens from 2 meters away will yield a soft, creamy background.
- Shooting the same portrait with a 24mm lens at f/2.8 from the same distance will keep more of the background in focus, even though both have the same aperture.
- However, if you move much closer with the 24mm, the background will start to blur more, but not as much as with the telephoto.
In practice, aperture and distance play just as big a role as focal length when controlling depth of field. It’s the combination that matters most.
Perspective Distortion: Warping and Compressing Space
Focal length also changes how space is perceived. Wide lenses exaggerate distance, sometimes creating distortion that makes objects up close look massive while backgrounds shrink away.
Meanwhile, telephoto lenses compress space, making background objects seem closer than they are. So when you see the sun looking huge behind a helicopter in an action movie, it’s shot with a telephoto lens.
Focal Lengths to Know:
Here are some good pointers for choosing the right lens. That being said, this also depends on your camera’s sensor size, which I’ll get back to in a minute.
- 24mm: Perfect for landscapes and establishing shots.
- 35mm: Versatile, great for dialogue and medium shots.
- 50mm: True-to-life perspective, the “nifty fifty.”
- 85mm: Portrait lens, ideal for isolating characters and adding intimacy.
Sensor Size and Its Impact on Field of View
The size of your camera’s sensor plays a crucial role in how focal length is perceived in terms of field of view. This effect is known as the crop factor.
A standard full-frame sensor (36mm x 24mm) captures the full angle of view of a lens. For example, a 50mm lens on a full-frame camera provides a natural perspective, similar to human vision.
However, smaller sensors like APS-C or Micro Four Thirds crop the image, effectively narrowing the field of view. An APS-C sensor has a crop factor of around 1.5x or 1.6x, which means a 50mm lens behaves more like a 75mm or 80mm lens in terms of what you see. Micro Four Thirds, with its 2x crop factor, makes that same 50mm look like a 100mm.
This is why cinematographers sometimes opt for wider lenses when shooting on smaller sensors, to compensate for that narrower field of view and capture more of the scene. If you’re aiming for the same composition as you’d get with a full-frame 24mm lens, you’d need something like a 16mm on an APS-C camera.
The crop factor doesn’t actually change the focal length of the lens, it changes the perceived field of view, which affects framing and depth perception in the final shot.
Summing Up
Choosing a lens isn’t just technical, it’s emotional. Wide angles immerse you in the scene; telephotos pull you back, making you an observer. It’s more than optics; it’s a storytelling choice.
Next time you frame a shot, think about what you want the audience to feel. Are they in the moment, or watching from afar? Your lens choice answers that question.
Read Next: Want to explore how lenses affect your shot?
Browse all lens-related articles, from focal length and bokeh to distortion, compression, and more.
Looking for a broader context? Visit the Cinematography section for composition, movement, and lighting techniques.
