What is Focal Length? (And Why it Matters in Photography!)
If you are new to photography, one of the first terms tossed at you is “focal length.” Are you buying a camera and lens? You have to decide on the focal length you want. If you are looking for a lens that zooms, there are many different focal lengths. How do you decide which focal length is best?
By the end of this article, you will understand what focal length is. We start with the scientific definition. It is for photographers who want to understand the inner workings of their cameras and lenses. But the practical implications of focal length are what matters to most photographers. So we will explore how different focal lengths affect the photos we take.
Focal Length Defined and Explained
So what is focal length? Let’s start with an optical definition of focal length. A focal length definition can get very technical. But for this article, let’s keep it as simple as possible.
Focal length is the distance between your camera’s sensor and the lens’s point of sharpest focus when focusing the camera to infinity.
How Focal Length is Measured
Your lens has many different pieces of glass. The elements interact to direct light into your camera. There is a point where light converges, or crosses, on the way to your sensor. That is the point of sharpest focus.
Lens manufacturers have done the testing and the math. They have measured the distance between this point of convergence and the camera’s sensor. That is the focal length of the lens. They label each lens with the focal length in millimeters (mm).
Take a look at this diagram showing the side view of a lens. Light comes into the front of the lens. It passes through many layers of glass with different shapes and curves. And these elements focus light to make a clearer image. In this example, the point of sharpest focus, or point of convergence, happens 28mm from the camera sensor. So this lens has a focal distance of 28mm.
How Focal Length is Standardized
The point of convergence changes as you focus closer or further away. But to standardize the measurement, the lens is tested by focusing it at infinity. When you focus on a point far in the distance, the light rays hit the lens almost parallel, as shown in the diagram. When focusing on a closer subject, light enters the lens at an angle. Your lens deals with this, but it affects how much of your scene is in focus. For more on this, see our article on depth of field in photography.
Focal Length in Practice
Now you know the official definition of focal length and how manufacturers measure it. But how do different focal lengths affect the way your photos look? Let’s see how focal lengths affect your photography in practice.
Angle of View
Focal length affects your angle of view. And your angle of view is how much of the world your camera lens can see. A lens with a shorter focal length, like 24mm, can see more of the scene than a lens with a long focal length, like 300mm. Lenses with smaller focal length numbers capture a more expansive view.
If you look straight in front of you, the area you can see is about 55°. That is your angle of view. You have a greater field of view with your peripheral vision. But off-center areas are not in focus. To see more of the world, you must turn your head.
A lens with a 43mm focal length captures a similar amount of the scene, about 53°. 50mm lenses are popular because they capture the world very close to how we see it. Photographers sometimes call a 50mm lens a “nifty-fifty.”
This table shows the angle of view for lenses with popular focal lengths.
Magnification
Focal length also affects how close objects seem to be. A lens with a long focal length magnifies objects making the subject appear closer. If you photograph far-away subjects, use a lens with a long focal length like 400mm or 800mm. Your angle of view is smaller, but magnification increases. The focal length of the lens determines how zoomed-in your photos look. The higher the number, the more zoomed your lens will be. Different focal lengths change how visually close the subject is.
Perspective Compression
Focal length also affects how objects look in relation to each other. Lenses with longer focal lengths compress the scene and make elements of the scene look closer together.
Compare these four photos of the same subject at different focal lengths. The three soup cans remained in the same position. They were spaced 10 inches (about 25cm) apart. The camera was moved back to keep the cans framed in the same way.
The cans seem to be spaced further apart at 24mm than 135mm. At 300mm, the cans seem to be almost next to each other. Also, notice the relative size of the cans. At 24mm, the front can is much more prominent than the others. At 300mm, the can in the back looks just as large, if not larger, than the cans in front. Remember, the cans were not moved.
This visual illusion is called “perspective compression.” Lenses with a longer focal length appear to compress objects. Lenses with shorter focal lengths add visual space between objects. You can choose which one is right for your scene.
Focal Length vs. Lens Length
Focal length has to do with the inner workings of a lens. It is not the physical length of a lens from the glass on the front element to the lens mount that attaches to your camera. Lenses can have the same focal length and be very different in physical size.
These two lenses cover the same focal lengths (16-35mm). But they have different internal constructions. For more information about how lenses are constructed, see beginners guide to camera lenses.”
How the Camera’s Sensor Affects Focal Length
The camera does not directly affect focal length. But the size of your camera’s sensor can impact how zoomed-in your photos appear. The scene of a lens attached to an APS-C (crop) sensor camera will look more zoomed-in than a lens with the same focal length attached to a full-frame camera. That is when a camera’s crop factor comes into play.
When determining their focal length, lenses are tested on cameras with a full-frame sensor. Full-frame cameras are equivalent to the once-popular 35mm film cameras and have become the standard for measuring focal length.
But some cameras have smaller sensors. For instance, many cameras have an APS-C sensor. It is about 1.5x smaller than a full-frame sensor. That is the crop factor of the camera. A lens with a focal length of 28mm looks the same as a 42mm lens when mounted on a camera with a smaller sensor. The perceived focal length is sometimes called the “equivalent’ or “effective” focal length.
All lenses are labeled with a focal length as though they were mounted on a full-frame camera. Even if the lens was designed for a crop sensor camera, that’s the case. It is not a problem if you have a crop sensor. You get used to how the lens looks on your camera. But if someone suggests that you use or buy a 50mm lens, know that it will be cropped on your camera. It will look like a 75mm lens.
If you want to know more about crop sensors, see our article on camera sensor size. This table shows the equivalent focal length and angle of view for lenses with popular focal lengths.
Zoom vs. Prime Lenses
Lenses are divided into two categories based on if they can change focal length. If a lens has one fixed focal length, it is a prime lens. If a lens can change focal lengths, it is a zoom lens. In general, prime lenses are sharper and often have a wider aperture.
Zoom lenses let you change the angle of view and magnification within a range of focal lengths. For instance, a 16-35mm zoom covers all focal lengths between 16mm and 35mm. You can choose 20mm, 24mm, or 30mm by twisting the lens barrel. That gives you a lot of versatility. Most variable focal length lenses get longer physically as you zoom. And lens manufacturers label zoom lenses by listing the shortest and longest focal lengths.
Grouping Focal Lengths
In photography, we group lenses by their focal length. For instance, lenses are wide-angle if they cover focal lengths of less than 35mm A telephoto lens is over 70mm.
Wide Angle Lenses (Less Than 35mm)
Lenses are wide-angle if they have a focal length of 35mm or less Wide-angle lenses capture a broad view of the world. The view is more comprehensive than you can see in one glance. Street photographers and photojournalists use lenses with shorter focal lengths. They can get close to their subjects, work indoors, and put themselves in tight spaces. These lenses capture the subject and the context.
Landscape photographers also love short focal lengths. They can capture large natural scenes like mountains and tall waterfalls. Landscape photographers take advantage of a wide-angle perspective. You can make a flower in the foreground look more prominent than the mountain in the background.
The widest lenses commonly used in movie production also fall into this range of focal lengths. Their field of view is ideal for showing plenty of the environment. And thanks to the wide aspect ratio, subjects can be far enough away not to appear distorted. But photographers rarely use lenses with short focal lengths for portraits. They enhance the perspective so much that facial features can look unnatural.
Ultra-Wide-Angle and Fisheye (Less than 16mm)
Lenses less than 16mm are sometimes referred to as “ultra-wide-angle.” A fisheye lens is an example of an ultra-wide-angle lens. These are often considered specialty lenses. They create such a wide angle of view that they feel unnatural and seem to distort reality.
Ultra-wide lenses are often used in event and architectural photography. They get a lot into a photo when shooting in a confined space. When used for journalistic scenes, ultra-wide-angle lenses can provide a dramatic, exciting angle—especially if you are close to the subject. A 16-35mm or 14-24mm zoom, for example, is a crucial tool in the bag of a press photographer.
A fisheye is an ultra-wide-angle lens that emphasizes wide-angle distortions. Fisheye lenses are usually between 4mm and 16mm and capture up to a 180° field of view.
Standard Lenses (35-70mm)
A standard lens has a focal length between 35mm and 70mm. These are the most common lenses, both in prime and zoom format. The focal lengths of the first lens that you got with your camera probably cover some, if not all, of this range.
Portrait photographers often use standard lenses 50mm, and 70mm are very popular. Lenses in this range best reproduce what our eyes see. They have minimal distortion. So they are suitable for documentary and street photography.
You can use lenses with standard focal lengths for virtually anything, from nature to action. If you want a good walking-around lens, buy one covering focal lengths between 35mm to 70mm. A popular standard zoom lens is 24-70mm.
Telephoto (70mm+) and Super-telephoto (200mm+)
Lenses are described as telephoto if they have a focal length of more than 70mm. Lenses longer than 200mm are sometimes referred to as “super-telephoto.” The lens is sometimes called a short telephoto if the focal length is between 70mm and 135mm. Currently, the longest telephoto lens in production is 800mm.
Photographers use telephoto lenses any time they are photographing something from a distance. Wildlife and sports photographers often use telephotos to bring their subjects closer. Landscape photographers use long focal length lenses to capture intimate landscapes. Remember, telephoto lenses compress the scene and make objects look closer together. That is not always what landscape photographers want.
Portrait photographers may also use telephoto lenses, like 85mms, if they take close-up shots. The lens compresses the subject, and they look leaner. It is often a flattering look. Many popular macro lenses also fall into the telephoto category. Photographers use macro lenses to photograph detail in extreme close-ups. A telephoto macro also gives you a little working space.
Best Focal Length for Your Photography
The best focal length for your photography depends on what type of photography you like to shoot. Let’s find the best focal lengths for each genre of photography.
Portrait Photography
The best focal lengths are between 50mm and 135mm if you like to photograph people. You can get standard prime lenses like 50mm with less distortion. Or you can buy a zoom lens covering the lower end of the range, like a 24-70mm or a 24-105mm. A short telephoto would also be a good buy for you. Many portrait photographers use a 70-200mm lens.
Street, Documentary, and Travel Photography
If you like to travel and take photos on the street, a standard lens is your friend. A 24-70mm lens is the go-to lens for many travel and street photographers. But many street and travel photographers like to use wide-angle prime or zoom lenses in the 16-35mm range. That lets them get in close and show a lot of the scene. If you are going into the unknown, you may want to look at a lens that covers a variety of situations, like a 24-105mm lens.
Architecture Photography
Architectural photographers often go with wide-angle focal lengths. They may shoot tall buildings on narrow streets. Or they may be inside an establishment trying to capture a tight corner or the majesty of a cathedral. A wide-angle lens works for it all. Architectural photographers may even pull out an ultra-wide-angle (12-24mm) lens or a fisheye when spaces get tight.
Sports and Wildlife Photography
Sports photographers and wildlife photographers share some common challenges. You may not be able to get close to your subjects, so a telephoto is a must. You need a 70-200mm or a 100-400mm lens. You may even need a super-telephoto lens if you are trying to photograph birds or players on a large field. And 800mm prime lenses are made for these situations.
Landscape Photography
Landscape photographers vary in their preferred lenses. You may like a wide-angle 16-35mm lens for grand landscapes. Or you may pick a telephoto lens like 100-400mm to capture details in the scene. If you like to photograph landscapes, you may need to try out a few different lenses to see what fits with your favorite landscape scenes.
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