Focal Length


Focal length, in the context of technology and particularly photography, refers to the distance between the camera lens and the image sensor (or film) when the subject is in sharp focus. It is usually measured in millimeters (mm) and helps determine the magnification, angle of view, and depth of field of the captured image. A lower focal length equates to a wider angle of view (wide-angle lens), while a higher focal length results in a narrower angle of view (telephoto lens).


The phonetic pronunciation of “Focal Length” is:/ˈfoʊ.kəl lɛŋθ/

Key Takeaways

  1. Focal length is a key determinant of a lens’ angle of view, magnification, and depth of field, with shorter focal lengths producing wider angles and deeper fields while longer focal lengths yield narrower angles and shallower fields.
  2. Prime lenses have fixed focal lengths, providing a single perspective that often leads to better optical quality and faster apertures, while zoom lenses offer variable focal lengths for greater versatility and the ability to adjust composition without changing your position.
  3. In digital photography, crop-sensor cameras affect the effective focal length, causing the field of view to appear narrower in comparison to full-frame cameras, which maintain the lens’ original focal length and perspective.


Focal length is an important term in technology, particularly in the fields of photography and optical engineering, because it provides insight into the characteristics of lenses and ultimately impacts image capture.

Focal length refers to the distance between a lens’s optical center and the image sensor or film plane when the lens is focused to infinity.

This measurement affects the angle of view, magnification, and perceived perspective in photographs.

Understanding focal length allows users to make informed decisions when selecting lenses, as varying focal lengths produce different results; for instance, wide-angle lenses (short focal lengths) are suitable for capturing vast landscapes, while telephoto lenses (long focal lengths) enable detailed close-ups or distant subjects.

In sum, focal length is crucial to lens functionality, image composition, and achieving the desired creative output.


Focal length is an essential attribute of a camera lens that directly influences the composition and perspective of captured images. Primarily, focal length serves to determine how zoomed in your subject will appear in relation to the scene. Technically, it is the distance between the lens and the image sensor (or film) when focused on infinity.

Measured in millimeters (mm), a lens with a short focal length produces a wider field of view, while a lens with a long focal length generates a narrower, magnified perspective. Photographers and videographers harness the power of focal length to create the desired visual effect, whether it’s capturing vast landscapes, vibrant street scenes, or intimate portraits, ensuring their creativity is accurately portrayed in the resulting images. Focal length also contributes to the depth of field, which is the range within an image that appears sharp and in focus.

A lens with a shorter focal length will generally have a deeper depth of field, keeping more of the scene in focus, while a lens with a longer focal length will have a shallower depth of field, making it effective for isolating subjects and producing a captivating bokeh effect. By understanding and experimenting with focal lengths, photographers can strategically select lenses that best suit their creative vision, bringing the world around them into focus with stunning accuracy and clarity. Whether you’re capturing immersive panoramas with a wide-angle lens or unveiling the hidden details of a distant object through a telephoto lens, the purposeful manipulation of focal length can evoke emotions and tell stories that transcend the boundaries of language and time.

Examples of Focal Length

Smartphones with Dual or Triple Lens Cameras: Modern smartphones often come with dual or triple lens cameras, each having a different focal length to provide various perspectives. For example, a smartphone could have a wide-angle lens with a short focal length (around 12-18mm) for capturing wider scenes, a standard lens with a medium focal length (around 24-35mm) for everyday photography, and a telephoto lens with a long focal length (around 50-85mm or more) for zooming in on distant objects. These various focal lengths allow users to capture diverse types of images without the need for external lenses.

Professional Photography: In professional photography, photographers use different camera lenses with varying focal lengths to create the desired composition and perspective in their images. For example, a portrait photographer may use a lens with a longer focal length (around 85mm) to create a flattering perspective and shallow depth of field, while a landscape photographer may choose a lens with a shorter focal length (around 16-35mm) to capture expansive scenes and maintain sharp focus throughout the image.

Security and Surveillance Cameras: Security and surveillance systems often use cameras with various focal lengths to monitor different areas effectively. A camera with a short focal length (wide-angle lens) can cover a large area such as a parking lot, while a camera with a longer focal length (telephoto lens) can be used for monitoring specific targets or license plates. By selecting the appropriate focal length, security professionals can ensure proper coverage and identification of potential security threats.

Focal Length FAQ

What is focal length in photography?

Focal length in photography refers to the distance between the camera lens and the image sensor. It is usually represented in millimeters and is an essential factor in determining the angle of view and magnification of an image. Different focal lengths are used for various types of photography, such as landscape, portrait, and macro photography.

How does focal length affect a photograph?

Focal length affects a photograph in several ways. It determines the angle of view (how much of a scene the camera captures), magnification (how large objects appear in the image), and depth of field (how much of the scene is in focus). A shorter focal length will yield a wider angle of view and less magnification, while a longer focal length will produce a narrower angle of view with higher magnification.

What is the difference between a prime lens and a zoom lens?

A prime lens has a fixed focal length, meaning it cannot zoom in or out to change its focal length. As a result, prime lenses typically have better image quality and a larger maximum aperture compared to zoom lenses. A zoom lens, on the other hand, has a variable focal length that allows you to adjust the lens for a range of focal lengths without changing the lens, providing greater versatility but potentially sacrificing some image quality.

How do I choose the best focal length for my needs?

Choosing the best focal length depends on the type of photography you are interested in. For landscape photography, you may want a wide-angle lens with shorter focal length (e.g., 14mm to 24mm) to capture vast scenes. Portrait photography often benefits from moderate focal lengths (e.g., 50mm to 85mm) for more flattering results. Sports and wildlife photography might require a telephoto lens with a longer focal length (e.g., 70mm to 400mm) for better subject magnification. It’s essential to consider your photographic requirements and experiment with different focal lengths to find what works best for your style.

What is the 35mm equivalent focal length?

The 35mm equivalent focal length is a standardized measure that allows photographers to compare focal lengths across different cameras and sensor sizes. It refers to how a focal length would behave on a 35mm film or a full-frame digital camera sensor. This measurement is particularly useful for those using cameras with smaller sensors, such as APS-C or Micro Four Thirds, as it helps to understand the field of view and depth of field for a given focal length relative to a full-frame camera.

Related Technology Terms

  • Aperture
  • Field of View
  • Lens Magnification
  • Depth of Field
  • Telephoto Lens

Sources for More Information


About The Authors

The DevX Technology Glossary is reviewed by technology experts and writers from our community. Terms and definitions continue to go under updates to stay relevant and up-to-date. These experts help us maintain the almost 10,000+ technology terms on DevX. Our reviewers have a strong technical background in software development, engineering, and startup businesses. They are experts with real-world experience working in the tech industry and academia.

See our full expert review panel.

These experts include:


About Our Editorial Process

At DevX, we’re dedicated to tech entrepreneurship. Our team closely follows industry shifts, new products, AI breakthroughs, technology trends, and funding announcements. Articles undergo thorough editing to ensure accuracy and clarity, reflecting DevX’s style and supporting entrepreneurs in the tech sphere.

See our full editorial policy.

More Technology Terms

Technology Glossary

Table of Contents