Some of the terms in photography can be a little confusing. Take focal length, for example. We know it refers to the lens on our camera, but what exactly is it? Understanding focal length will help you know which lens to purchase and how to use it for a wide variety of photographic applications.
Which Type of Focal-Length Lens to Use for Each Situation
- Wide-angle lens (short focal length): A short focal length (wide-angle) lens takes in more of the scene than what is perceived by the human eye. It provides a wider field of view or angle of view. 8mm to 35mm are common focal lengths.
- Normal lens: A focal length that corresponds to the human eye. 50mm, also known as the Nifty Fifty.
- Telephoto lens (long focal length): A longer focal-length lens than normal, this lens allows one to get close up with being closer. It provides a narrower field of view than a normal lens. Focal lengths are 85mm to 2000mm.
- Portrait lens: This is a telephoto lens, usually with a little bit longer focal length than normal. 85mm, 100mm, 135mm are often used for portraits. Other focal lengths can be used, too.
- Landscape lens: For that sweeping vista, many gravitate toward wide-angle lenses for landscapes and cityscapes. Typical focal lengths are 20mm, 24mm, 28mm.
- Macro lens: These lenses can be of any focal length, but most often are in the normal or short telephoto range of focal lengths.
- Zoom lens: Zoom refers to the lens being able to change the focal length. It can be a wide-angle zoom lens, a normal zoom lens, a telephoto zoom lens, or a combination of lenses. Focal lengths are 16-35mm, 24-85mm, 70-200mm, 150-500mm.
- All-In-One lens: For many beginners, this may be the perfect first lens. The lens is capable of wide angle, normal, short and long focal length telephoto, and even macro. Focal length ranges between 24-300mm.
- Prime lens: This is a fixed focal length lens, and often has premium features. Available focal lengths are 8mm, 24mm, 35mm, 50mm, 85mm, 105mm, 200mm, 500mm.
What Is Focal Length?
Focal length is often used to describe the size of the lens. This optical measurement refers to the shape of the lens, not its physical dimensions. A technical definition of lens size is the distance between the rear nodal point and the focal point of the lens, while the lens is focused to infinity. In other words, it is determined by the distance between the lens and the image sensor when the subject is in focus. Focal length is generally represented in millimeters, usually abbreviated as mm. This tells us the angle of view for a given lens, or how much of a scene will be captured using that lens.
For all intents and purposes, the focal length is how “zoomed in” your images appear. The smaller the focal length, the wider the field of view. The higher the number, the more narrow or “zoomed in” your angle of view will be. In addition to measurement in millimeters, lenses are often referred to as a wide-angle lens, normal lens, telephoto lens, long focal length lens, short focal length lens, or as a zoom lens.
This discussion will be based on 35mm full-frame cameras. Other sensor sizes will have a crop factor to consider, which will also be discussed.
A wide-angle lens has a short focal length and is generally characterized by the wider than normal field of view, also referred to as the angle of view. At very wide focal lengths, the image can appear distorted and fisheyed. Careful use of subject placement can eliminate or limit distortion effects. The optical properties of short focal length lenses also allow for creativity in the use of depth of field or depth of focus. Understanding the f-stop or aperture is important when using this type of lens.
The wider angle of view doesn’t have to be extreme. That depends on just how wide you want to go. A lens just a little bit wider than normal can help your photographs capture more of the scene without introducing a curved-edge effect. Even an ultra-wide distortion effect can be utilized in a way that enhances the final image.
What is the focal length of a wide-angle lens? Basically, anything shorter than normal. 8mm to 35mm is considered wide-angle on a full-frame camera. A wide-angle lens with a focal length of 35mm, 28mm, or even 24mm won’t look particularly wide. Shorter focal lengths, however, can make things more difficult. The line-lengthening distortion can really contort a person’s face, exaggerating their features. This is why photographers generally don’t reach for a wide-angle lens when taking portraits. For architectural and real estate photography, though, the wider field of view may allow us to show the entire scope of a room or structure. Wide-angle lenses are often used with landscape photography as well.
What is normal, anyway? We’re not talking psychiatry here. Rather, it refers to the focal length of the human eye. By applying the definition of focal length to the human eye and comparing it to a lens on a 35mm camera, the result is a number in the 50mm range.
It’s actually more involved than that, but a 50mm lens works well as the focal length to give a natural perspective and field of view to our images. A normal lens for any format is more or less equal to the diagonal measurement of the image format. For a 35mm full-frame format, the image sensor (or film) area is a rectangle 24mm by 36mm. So, the “normal” lens would technically be about 43mm. A 50mm lens is close to that length and easy to manufacture. It produces a natural looking perspective and has become known as the Nifty Fifty lens.
It’s Nifty partly because it is a fast lens, allowing one to use it in lower light or with different ISO settings. Understanding ISO and knowing how shutter speeds and f-stops relate to one another in the Golden Triangle is an important step for any photographer. Most beginners especially benefit from this knowledge. The name Nifty is also due to the smaller size and lower price compared to lenses of other focal lengths. Lenses included with most digital cameras have a normal focal length.
The word telephoto technically applies to a specific design of long focal-length lenses, but the term has broadened and is now essentially synonymous with any long focal-length lens. A long, focal-length lens will narrow the angle of view and cause apparent image magnification. In other words, it brings the subject closer. When most people talk about zooming in on a subject, they generally mean using a longer lens.
What is the focal length of a telephoto lens? For a full-frame 35mm camera, any lens longer than the normal 50mm range. The focal length of a telephoto lens can range between 85mm and 2000mm or more. Popular lenses in this range include 85mm, 100mm, 105mm, 135mm, 200mm, or longer. Zoom lenses are typically in the 70-200mm and 150-500mm range.
Telephoto lenses have optical properties that foreshorten perspective, which make them a good choice for portrait lenses. They also have less depth of focus than shorter focal length lenses, which can cause interesting selective-focus effects. When a photographer talks about bokeh in a lens, they are referring to the blurring of out-of-focus elements of the image, an effect easily achieved with a long focal-length lens.
A lens that captures a person’s head and shoulders is called a portrait lens. Typically, a portrait photographer will choose a short telephoto lens in the 85mm or 105mm range. While a normal or wide-angle lens can also be used, the slight foreshortening of the narrower angle of view, coupled with the ability to blur the background makes the short telephoto lens perfect for a head and shoulders portrait.
Many kit lenses will reach a focal length that enters portrait lens territory, but a prime lens in that focal length is often faster and gives us more control over bokeh and selective focus. Some of these lenses are among the sharpest lenses around. The cost of certain models can cause us to grasp, but so does the image quality they produce.
As with the portrait lens, a landscape lens can be of any focal length. But for those majestic, sweeping vistas we seek out while traveling cross country, many photographers gravitate towards shorter focal-length lenses, preferring their wider angle. With a wide-angle lens, more of the scene can fit into the image area, and it’s easier to create an impressive depth of field.
What is the focal length of a landscape lens? The wider the angle, the more scenery we can fit into the frame. Therefore, focal lengths such as 20mm, 24mm, and 28mm are common choices, though a normal lens can also work.
Macro lenses are specialty lenses which have been optically designed for ultra-close focusing. A macro lens with a longer focal length allows the photographer to achieve the same magnification ratio of a shorter lens, but from a greater camera distance. This makes it easier to add lights if necessary. A macro lens of any focal length has a very narrow depth of focus when focused extremely close, but this is especially true with a long focal-length macro lens.
Focal lengths common to macro lenses are 50mm, 60mm, 100mm, and occasionally 200mm. Some are even designed with a built-in flash to aid in exposure. Many zoom lenses have a feature known as macro focusing, but very few zoom lenses can focus as close as a true macro lens.
Beginner photographers are often confused by zoom lenses. To many people, a zoom lens is a telephoto lens, since you can “zoom in” on a subject. But in simplest terms, a zoom lens can change focal lengths, while a telephoto lens cannot.
A zoom lens can adjust its range to be wide-angle or long telephoto. And it’s not enough to simply say “wide-angle” because the term encompasses a variety of focal lengths between 16mm and 35mm. A zoom lens may not be telephoto at the longest focal length, but can still achieve wide-angle under 50mm of the normal lens. Zoom lenses are all different, making their focal lengths ambiguous.
So, to avoid confusion, many manufacturers and photographers will use additional words to accurately describe the zoom lens. We mentioned wide-angle zooms, which are commonly 16-35mm or 20-40mm. A normal-range zoom lens, like many kit lenses, maybe 24-85mm or 28-105mm. For a while, 35-70mm was almost as common as the Nifty Fifty lens. A telephoto zoom lens could describe 70-200mm, 70mm or 100-300mm, or 70-150mm. And ultra telephoto zoom could be 150mm, 200-500mm, or 650mm.
All-In-One lenses have become a very popular type of zoom lens, especially for crop-sensor digital cameras. This lens allows the photographer to take almost any type of photo using a single lens. The lens can range from significantly wide-angle, to long telephoto, and can even approach near-macro focusing ability.
What is the focal length of an all-in-one lens? For the full-frame format, the range is typically 24-200mm or 35-300mm. In a crop-sensor camera format, the lens can have even more range and still be a reasonable size, weight, and cost. Most crop-sensor cameras are in the 18-300mm range.
There are some limits to these lenses, though. To keep size, weight, and costs down, all-in-one lenses are unlikely to be very fast, meaning they won’t have a large aperture. Even though image quality can be good, they are generally not as sharp as other lenses across the focal lengths.
A prime lens has only one focal length. It can be wide-angle, telephoto, normal, or macro. Photographers who choose prime lenses are looking for are ultra-high image quality or very fast f-stops.
It’s not unusual to see prime lenses of virtually any focal length. A fisheye 8mm is a prime lens, as is a 24mm f/1.4 or 50mm f/0.95. Other prime lenses may be telephoto lenses such as a 500mm f/2.8 lens or a 2000mm f/11. What they all have in common is superior image quality, a fast aperture or f-stop, and a very high price.
There are some modest prime lenses, such as a 50mm f/1.8, 35mm f/2.8, or 135mm f/3.5. These lenses are smaller, lighter, and not nearly as expensive as the premium prime lenses, and yet can still deliver some very fine results.
What Is a Crop-Sensor Camera?
In this discussion, we’ve mentioned crop sensor a few times. What does it mean?
A crop-sensor camera, as the name implies has a smaller (or cropped) sensor than its 35mm full-frame sensor counterpart. The most noticeable difference associated with this sensor is its “crop factor.” The crop factor refers to the magnification of the field of view when looking through the viewfinder.
Crop-factor digital cameras are some of the most heavily produced DSLR and ILC cameras on the market. Crop-factor cameras also tend to be lower priced than full-frame cameras. With the superb quality of the brands available today, crop-sensor cameras have a very large market share and will be around for a long time. Many of the crop-sensor digital cameras are better than the expensive film and photography cameras from just a few years ago. Yes, this is a very good time to be a photographer!
The most common crop-sensor format is the APS-C format with a crop factor of 1.5x. Another very popular format for digital cameras is the 4/3rds or micro 4/3rds (MFT) format with a 2x crop factor.
Let’s compare the difference between a crop-sensor camera (1.5x crop factor) and a full-frame sensor. A 50mm lens on a full-frame sensor camera will have a field of view of 50mm. A 50mm lens on a crop-sensor camera has an apparent field of view of 75mm, since 50mm x 1.5 = 75mm. In layman’s terms, your 50mm lens will “feel and act” like a 75mm lens when on a crop sensor camera.
The crop factor allows for camera and lens makers to offer some very interesting lens choices. Besides the standard kit lenses of 18-55mm or so, the all-in-one lenses are also available at reasonable prices. It’s not unusual to see 18-300mm in an APS-C format lens. With a crop-sensor, telephoto lenses can become super telephoto lenses! A 150-600mm lens ends up delivering the equivalent field of view and magnification of a 900mm lens on a full frame sensor camera. Imagine adapting a 2000mm amateur astronomy telescope to an APS-C or even an MFT sensor camera. That equates to an extreme telephoto of 3000mm or 4000mm. Wow, indeed.
The same thing is true with larger format cameras but in reverse. A medium format camera may have a normal lens in the focal length of 80mm or even 100mm, depending on the size of the format. In large format film cameras, the crop factor in reverse gives us normal lenses in the 150mm and 210mm range. Certain professional users require these larger formats. Some photographers may enjoy this format simply because of their love of this art form. If you find yourself venturing into this fantastic field, more power to you. Just be prepared to spend a lot of time and money on these larger formats.
What Are Compression, Bokeh, and Depth of Field?
We’ve mentioned these terms a few times in this article. A more comprehensive tutorial is available on Cole’s Classroom.
In a nutshell, longer focal lengths (the higher number of millimeters) cause compression. Compression is a phenomenon produced by longer focal-length lenses in which the background seems to be flattened out and pulled closer to a subject. Lens compression can enhance the bokeh and background blur in your images, an effect sought by many portrait photographers, or anyone who wishes to isolate a subject from the surroundings.
A wider angle, short focal length produces the opposite effect. It can make it seem as though the landscape or cityscape goes on forever. The great depth of focus achieved by using small apertures in a wide-angle lens can draw viewers closer, making them feel as if they are inside your image.
What Do You Want from Your Lenses?
Are you ready to experiment with different lenses? A prime lens could allow you to create stunning works of art with the highest image quality imaginable. Other prime lenses could give you the ability to capture elusive and rare wildlife or let you document a world-record event in competitive sports.
Choosing the right focal length will depend entirely on what it is you are trying to capture. Are you looking to capture landscapes, lifestyle, or portraits? As you develop your personal style, your lens preferences will likely change. Maybe you want to create images of bugs and flowers. Perhaps your family vacation is your subject matter. Or maybe you have a photography job in the real estate or wedding industries.
To find the focal length that is right for you, experiment and try out different lenses until you find the length that best suits you and your shooting style. Who doesn’t love to try out lenses anyway? Have fun with it!
The bottom line is, photography is fun. A person can shoot for an entire lifetime and never stop learning the art and craft of photography. At Cole’s Classroom, we’re more than happy to assist you along the way.