Understanding focal length helps photographers determine what lenses to invest in and which lens to use on a particular shoot. Focal length describes one of the primary characteristics of a lens. And it plays a critical role in how we execute our creative vision.
In this article, we define the focal length and angle of view. In addition, we look at how these factors interact. We also explore the visual characteristics of various focal lengths, the relationship of focal length to depth of field, and how it alters perspective.
Also, we hope to clarify some of the more confusing aspects of this topic when sensor size and crop factor are brought into play. For now, our discussion of focal lengths will be based on a full-frame camera. We’ll get into full frame and crop sensor camera formats in more detail later in this article.
What is Focal Length?
Focal length measures the distance between the optical center of a lens – the focal point where the light rays converge – and the image sensor. We measure any given focal length in millimeters, abbreviated mm, with the lens focused to infinity. It is a technical characteristic of the lens, regardless of the manufacturer or camera format, and determines the angle of view.
The diagram below illustrates the relationship between focal length and angle of view.
How Does Focal Length Affect Angle of View
The focal length of a lens determines the angle of view, also known as the field of view. In other words, it’s how much of a scene the camera’s sensor captures. A shorter focal length, such as that of a 24 mm lens, produces a wide angle of view. The area captured is large while the subject will appear small.
In contrast, a long focal length, such as a telephoto lens, results in a narrow angle of view. It captures a smaller area, but the subject appears larger. Furthermore, longer focal lengths compress the image, making the background appear closer and larger than it would with a standard lens.
Focal Length Comparison
The graphic below illustrates how focal length determines the angle of view.
A lens with a focal length of 11 mm, shown at the right of the diagram, is an extreme wide angle lens, or fisheye lens. It produces a 180 degree angle of view.
A 28 mm wide angle lens with its short focal length produces an angle of view of 74 degrees. These lenses are generally deployed for landscape photography.
An increase in focal length to 50 mm drops the angle of view to 46 degrees. Its field of view most closely matches that of the human eye.
At the far left of the graphic, the 900 mm lens, narrows the angle of view to just three degrees. Focal lengths greater than 300 mm are considered super telephoto lenses.
What is the Best Focal Length for My Shot?
The best focal length, or the right focal length, depends on your creative vision.
The photos below illustrate how focal length affects what the image sensor captures.
Some lens focal lengths fulfill specific needs better than others. So, let’s look at the spectrum of focal lengths and how they meet those specific needs. This helps us in finding the right focal length for a particular shoot.
Ultra Wide Angle Lenses, AKA the Fisheye
These lenses come with short focal lengths in the 8-15 mm range, giving them a wide angle of view, from 100 – 180 degrees. And some specialized fisheye lenses expand that up to 280 degrees.
Two Distinct Categories of Fisheye Lenses
The diagonal fisheye captures its full angle of view in the horizontal plane only and fills the entire frame, as shown below.
Meanwhile, the circular fisheye captures its full angle of view both horizontally and vertically. This produces a complete circle within the frame, surrounded by black, as demonstrated in the image below.
These shorter focal lengths create an extreme bend in the image, sometimes to the point of abstraction. And some photographers exploit this to great effect. Others consider it a novelty. In recent years, the fisheye gained favor with extreme sports photographers, where the distortion due to the short focal lengths adds to the sense of motion.
In addition, ultra wide lenses have scientific applications. For example, photographers capturing polar light rays or recording solar radiation use these lenses.
What is Wide Angle and Standard Wide Angle?
In general, any lens focal length less than 50 mm is considered a wide angle. More specifically, lenses with a focal length 16-24 mm are wide angle while those from 24-35 mm are standard wide angles. The field of view is wider than what the human eye normally sees and along with an excellent depth of field, wide angle lenses developed a must-have status for landscape photographers.
But there’s more. Perspective changes with the short focal length of a wide lens. Objects near the camera appear disproportionately bigger than objects in the distance. A portrait taken with a wide angle lens renders a person’s – or a horse’s – nose unnaturally pronounced.
Wide angle lenses also introduce some distortion. Parallel lines converge due to the wider angle. Photographers find creative ways to make use of this distortion.
What is a Standard Lens
Sometimes called the normal lens, the standard lens focal length measures approximately 50 mm. Some sources refer to any focal length between 35 mm and 85 mm as standard lenses. This lens focal length closely simulates the natural perspective of humans and, coupled with sharp image capability and minimal distortion makes them popular for a variety of photographic genres.
Lenses with standard focal lengths find their niche in travel, street, floral, and portrait photography. It can also be useful for landscape photography. Often called the “nifty fifty,” a quality 50 mm lens excels in multiple photography roles.
Of all the camera lenses, if you were going to work with just one, a standard focal length lens in the range of 50 – 55 mm would be a good choice.
Some photographers consider a lens with a focal length longer than 70 mm to be a telephoto lens. Others put that number at 100 mm or 135 mm.
A telephoto lens becomes essential when you want to get close to a subject from a distance and to get physically close is either dangerous or socially impolite.
Macro and Portrait Lenses
Lenses with a focal length between 70 – 150 mm find a niche in macro and portrait photography. Macro lenses allow extreme close-up images. Below, an image of an insect shows the close-up capability of a macro lens.
Telephoto lenses produce a shallow depth of field, resulting in a blurred background or bokeh. Also, the longer focal lengths result in lens compression, creating a background that appears closer than it actually is.
Long focal lengths of 300 mm and up rank as super telephoto lenses. These long focal length lenses excel at wildlife and sports photography.
A super telephoto lens poses a special challenge for photographers. Just a slight movement of the camera results in large and rapid changes in what you see in the viewfinder – a different experience than using normal lenses. So photographing the erratic movements of a bird in flight or the shifting motion of an athletic event requires a unique skill.
Other Super Telephoto Considerations
Combining longer focal length with good image quality commands high prices. A 600 mm lens for the Nikon Z series cameras sells for around $15,000 (US).
Also, you might consider weight. A super telephoto lens may weigh upwards of 10 pounds. It’s like carrying a couple of bricks.
The Difference Between Prime Lenses and Zoom lenses
A prime lens comes with just one focal length. The focal length examples discussed above centered on prime lenses.
Meanwhile, a zoom lens has a variable focal length. A 70-300 mm lens covers a focal length range from just above the standard lens to just short of super telephoto.
Which is Better? Prime or Zoom?
When it comes to image quality, prime lenses are superior. A prime lens contains fewer optical elements, reducing the chances of anomalies like chromatic aberration, vignetting, and distortion.
The fixed focal length means a minimum number of moving parts in a prime lens, resulting in sharp focus. In addition, prime lenses allow more light into the camera due to a wider maximum aperture. So photographers can shoot at higher shutter speeds.
A Word on Behalf of the Zoom Lens
Zoom lenses offer versatility to the photographer. Simply rotate the zoom ring to change focal lengths and the corresponding angle of view. Compose and crop photographs in-camera and capture various perspectives.
The zoom lens proves essential for wedding photography and photojournalism where being able to capture the action in the moment is critical. Image quality is a consideration; however, lens manufacturers continually expand and update their product lines. As a result, high-end zoom lenses deliver image quality to rival prime lenses.
With just a couple of lenses, you cover a broad range of different focal lengths. Also, it saves time by not having to change lenses and reduces the possibility of dust landing on the camera sensor.
Full Frame Camera Sensor or Crop Sensor
Full frame designates a digital camera with a 35 mm image sensor, which measures 36 mm by 24 mm – a ratio of 3 – 2. The terminology stems from the days of analog photography when 35 mm film was a standard format.
The crop sensor, called the Advanced Photo System Type-C, or APS-C sensor, has the same 3 – 2 aspect ratio as a full frame but is smaller. It may have a crop factor of 1.5x or 1.6x, depending on the camera manufacturer. Canon uses the 1.6x crop factor, Nikon the 1.5x.
Another size, the micro four-thirds (MFT) sensor is used by Olympus and Panasonic. Its crop factor is 2x with an aspect ratio of 4 – 3 and is smaller than the APS-C sensor.
The graphic below illustrates the relative sizes of these three sensors.
For more information on full frame vs. crop sensor cameras, please read our detailed article here.
Sensor Size in a Medium Format Camera
This format utilizes a sensor that mimics the 120 mm film cameras. The sensor size varies with the camera manufacturer, from 43.8×32.9 mm to 53.7×40.2 mm. The aspect ratio is 4 – 3. Fuji, Hasselblad, and Leica produce medium format cameras that are used extensively in advertising and fashion photography.
How Sensor Size Affects Focal Length
Sensor size determines the equivalent focal length of a lens. A 50 mm lens on a full frame camera performs like a 50 mm lens. A 50 mm lens on a camera with a 1.5x crop factor, such as a Nikon DX camera, equals an equivalent focal length of 75 mm.
On a camera with a 1.6x crop factor, such as the Canon EOS M50 Mark II, a lens with a focal length of 50 mm performs like an 80 mm lens.
Check the camera’s specifications page to find details about sensor size, and you’ll be able to determine the effective focal length of any lens.
In Conclusion: What’s Important
As a photographer, it’s not absolutely essential to know the technical details of focal length and field of view. However, knowing how a particular lens renders the subject helps in achieving your creative vision.
You may take advantage of the distortion in a wider angle lens to achieve a certain look. In another setting, the focal distance of a telephoto lens blurs the background, adding emphasis to the subject.
Working with an interchangeable lens camera, a variety of quality prime lenses enables you to deliver a quality product in diverse settings. If a quick reaction is important, a zoom lens empowers a photographer to adapt to the proper focal length in an instant. And for a general walk-around camera lens, the 50 mm is a favorite among photographers.
Since photographic optics are expensive, it pays to understand how a particular lens serves your purposes before you purchase. A camera performs only as well as the lens on its front. So understanding the diverse range of focal length lenses goes a long way to helping you achieve your artistic and professional goals.