Understanding Focal Length in Photography: The Ultimate Beginner's Guide

Focal length is the distance between the center of the lens and where light converges to create a sharp, detailed image on the camera’s sensor.

A lens’ focal length affects how much of a scene is in view in the frame – the field of view. And the second major impact is on magnification. Lenses with longer focal lengths magnify subjects but in doing so they narrow the field of view.

Photographers have lenses available to them with focal lengths from around 14mm to 800mm or more, though the most commonly used lenses are 35mm, 50mm, 85mm, telephoto lenses of 200mm and 300mm, and zoom lenses of 24-70mm and 70-200mm.

What Is Focal Length in Photography?

The focal length of a camera lens is the distance between the lens and the light sensor when the subject is in focus. More technically, it is the point where light converges within the lens and the image sensor when focused on your subject. Focal length is usually measured in millimeters (mm) and determines the angle of view and how much of the scene will be captured.

The focal length also affects the magnification of the image – or how large the components of the image will appear. Shorter focal lengths result in images with a wider field of view. So if, for instance, you were taking a photo of a mountain range, you would see more individual peaks in your photo, but each one would appear smaller and have less detail than if you were using a lens with a longer focal length.

Remember: Focal length does not refer to the physical length of the lens. Focal length is a measurement of the optical distance within the lens; physical length, of course, is the actual length of the lens, though it is true that zoom lenses have both longer potential focal length and longer lens bodies. A 35mm lens, referring to its focal length, can range in physical length from one manufacturer or model to the next.

What are the Differences Between a Zoom Lens and a Prime Lens?

The key difference between the two lens types is that prime lenses only have one focal length, for example 50mm or 85mm, while zoom lenses cover a range of focal lengths, for example 24-70mm or 70-200mm.

The variable focal length of zoom lenses is usually achieved by additional lens elements that shift the distance between light convergence and the sensor. Prime lenses have a fixed focal length. To change the focal length of an image if you’re using prime lenses, you must change the lens on your camera.

Which is better? Zoom lenses can be less hassle because you don’t have to change a lens to adjust focal length. But there’s a tradeoff for the versatility of zoom lenses. Prime lenses are lighter because they have fewer optical elements. They tend to have less optical distortion, less chromatic aberration, and are usually brighter (that is, they have a larger maximum aperture) than zoom lenses.

What Is the Importance of Focal Length?

Focal length has a huge effect on your image! The focal length dictates the field of view that your sensor captures. The lenses with the longest focal lengths (called telephoto) have a very narrow field of view and are able to capture details on objects from greater distances. Telephoto lenses are popular for wildlife and sports.

Lenses with the shortest focal lengths (called wide-angle lenses or sometimes fisheye lenses) have a very wide field of view. They are ideal for capturing expansive scenes, such as landscapes, astrophotography, architecture, and interiors. Wide-angle lenses emphasize depth and distance in a scene, often creating a dynamic and immersive effect. They can also exaggerate perspective, making foreground objects appear larger and more prominent relative to the background.

Field of view is measured in degrees. The widest lenses, called fish-eye, can capture a field of view of as much as 180 degrees. This means that objects as much as 90 degrees from the front lens element will be captured in the image.

Note: Watch out for distortions with wide-angle lenses. Straight lines near the edges of the frame can appear curved, and subjects close to the lens can appear stretched or disproportionately large.

• 35mm lens: Note the width and height of the image taken with a 35mm lens, which is considered wide angle because it has a wider perspective than the human eye.To see this much with your eyes, you would have to turn slightly from side to side.

• 50mm lensThe image taken with a 50mm lens is about the same field of view as the human eye.

• 85mm lensThe image is more concentrated on the center of what you’d naturally see with your eyes.

• 135mm lens Narrowest field of view but best detail.

How Does Focal Length Affect Lens Size?

Lenses with longer focal lengths are usually physically longer and heavier than standard or wide-angle lenses. This is because the front lens element needs to be farther away from the sensor to move the light convergence away from the sensor.

This is easy to see in zoom lenses that do not zoom internally. At longer focal lengths, the front lens element telescopes forward, away from the camera sensor. When adjusting to wider angles, the front lens element retracts into the barrel of the lens to reduce the focal length.

Telephoto lenses often have complex designs with more glass and moving parts, resulting in heavier lenses. For example, the Canon EF 70-200mm f/4L IS II USM telephoto lens weighs about 1.7 pounds, while Canon’s EF-S 18-55mm f/3.5-5.6 IS wide angle lens weighs only about 7 ounces.

What is the Difference Between Adjusting Focal Length and Cropping?

The difference is that adjusting focal length is an optical method for capturing the image; cropping edits the image after it has been captured. Using a longer focal length and cropping are two ways to achieve the effect of a narrower field of view in the final image, effectively making the subject appear closer.

Adjusting focal length is achieved during the shoot by changing lenses or by using a zoom lens and zooming in or out to get the preferred focal length. Cropping an image is a step taken in editing the image after the shoot.

Cropping an image in post editing can achieve the same field of view, but you sacrifice the resolution of any pixels that are cropped out. Depending upon how you plan to use the image, you may or may not notice this loss of resolution. However, for the best quality and to use the full resolution of your sensor, it is usually best to select a focal length that optically offers the field of view you want to capture, rather than cropping in post.

How Does the Camera Sensor Size Affect a Photo’s Field of View?

Sensor size has a major impact on an image’s field of view - whether it is full frame or cropped. Smaller sensors have a narrower field of view than larger sensors for the same focal length, giving the image a zoom factor.

Full-frame sensors are approximately 36mm x 24mm. With these sensors, camera lenses keep their true focal length and field of view. For example, a 50mm lens on a full-frame sensor delivers a full field of view with no cropping.

Crop sensors are smaller sensors approximately 22mm x 15mm. They deliver a much reduced field of view. For instance, an APS-C sized sensor, which is smaller than a “full frame” 35mm sensor, will capture images with approximately 1.5x narrower field of view. In this setup, the field of view on a 50mm lens is 75mm, which is like zooming in on the subject, narrowing the field of view.

Another type of crop sensor is a micro four thirds sensor with a size of 17mm x 13mm and a crop factor of 2x, so that images through a 50mm lens appear as if taken through a 100mm lens.

What are Effective Focal Length and Crop Factor?

Effective focal length is the focal length of a lens when employed on a full-frame camera as compared to using the lens on a camera with a smaller sensor. When a lens is switched from a full-frame camera to a camera with a crop sensor, the effective focal length gets longer by a factor such as 1.5x or 2x.

APS-C sensors are sometimes referred to as “crop factor.”

Although there is no actual cropping being performed (the full resolution of the sensor is being utilized), this provides an easy way of conceptualizing the comparison between two different sensor sizes and how they will capture images from the same focal length. If you are familiar with how a full frame 35mm captures images with various focal lengths, you can multiply your lens’s focal length by 1.5x and this will approximate the equivalent field of view that an APS-C sensor will capture.

A 33mm lens paired with an APS-C sensor has an effective focal length roughly equivalent to a 50mm lens paired with a full frame 35mm sensor, an increase of 1.5x.

Discussion of appropriate focal lengths for various subjects assumes a 35mm sensor. Divide by your sensor’s crop factor (e.g. 1.5 for APS-C) to calculate the equivalent focal length for your sensor.

What Are Types of Lenses as Measured by Focal Length?

Understanding focal length is essential when choosing the best lens for your purposes in composing your shot to get the desired results:

• Standard lenses, aka normal lenses, have a normal focal length typically about 50mm. The popular 50mm size being the lens size that sees the world or has a field of view most similar to that of the human eye.

• Wide-angle lenses have short focal lengths of 16mm, 24mm and 35mm with a wider field of view.

• Ultra-wide angle lenses have even shorter focal lengths from 10-24mm producing an ultra-wide field of view.

What is the Best Focal Length for Portraits?

Lenses from 50mm to 135mm are the best focal length range for portraits, and 85mm is the most popular focal length, combining the advantages of 50mm perspective and longer focal length lenses. An 85mm lens gives a natural perspective with a good working distance. It can also produce bokeh in the background when you want to use blur to isolate the subject.

A 50mm is a good focal length for medium to wide portraits, typically producing little barrel distortion that could make your subject appear unnatural. This focal length is often used in environmental portraits where the background is important to the shot. 100mm or 105mm and longer can be great for outdoor portrait photography where you can get plenty of distance between you and your subject to frame your shot. These focal lengths reduce facial distortion and give you the option of more bokeh and background compression. A 135mm lens is excellent for headshots.

What is the Best Focal Length for Landscape Photography?

20mm to 35mm is generally good for landscapes when you want to capture a whole scene in one frame. Wider than this tends to introduce distortion (the fisheye effect). However, longer focal lengths (70mm-200mm) allows you to focus in on specific details of your scene for more dramatic images.

The best focal lengths for landscape photos range from 14mm to 35mm depending on the landscape scene and the results you want to achieve.

Ultra-wide lenses in the 14mm to 20mm range are great for wide views and vistas, taking in a vast landscape scene. You get more of the total picture with these wide-angle lenses, but some distortion is possible. Moving to a 35mm lens offers versatility and a natural perspective, but you don’t get as wide a shot.

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