Some of the terms in photography can be a little confusing. Take focal length, for example. We know focal length refers to the lens on our camera, but what exactly is focal length? Understanding focal length will help you know which lens to purchase and how to use it for a wide variety of photographic applications.
What is Focal Length?
We often use focal lengths 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, focal length is determined by the distance between the lens and the image sensor when the subject is in focus. A lens’ focal length is generally represented in millimeters, usually abbreviated as mm. This tells us the angle of view or view of field for a given focal length lens, or how much of a scene will be captured using that lens.
So what’s a focal length described in basic terms? It represents how “zoomed” in your image will appear to you. The longer the focal length, the closer your subject appears to you when you look through the viewfinder. The shorter the focal length, the more you are “zoomed out” or get a wider field of view.
In addition to measurement in millimeters, lenses are often referred to as a wide-angle lens, normal lens, long lens, short lens, or as zoom lenses.
This discussion will be based on 35mm full-frame cameras. Other sizes will have a crop factor to consider, which will also be discussed.
What is Short Focal Length?
Lenses with short focal lengths take on a broader angle of view and lower the magnification. Focal lengths with smaller numbers can show more of the scene, and make subjects appear smaller in the frame than they do to the human eyes.
Additionally, lenses with a short focal length widen or expand a perspective, resulting in more space between the elements in a picture. Lenses with a short focal length have a larger depth of field, letting you focus on a wider range of elements.
Landscape and architecture photographers typically use a short focal length so that they can get more of their subject/s to fit the frame.
What is Long Focal Length?
Lenses with longer focal lengths create a narrower angle of view, letting you increase image magnification. Focal lengths with larger numbers make subjects appear larger compared to how the human eyes perceive them.
Moreover, the longer the focal length of a lens, the more elements stack within the frame, causing a photo to have a compressive perspective. These focal length lenses can create a shallow depth of field, allowing you to focus on small objects at particular distances or make distant subjects closer.
Sports and wildlife photographers usually use a long focal length so that they can get a close-up shot of their subject/s without physically getting close.
Focal Distance vs. Focal Length
Focal length, as discussed above, is the distance between the lens and the image sensor. It’s that property of a camera lens that determines how wide or narrow the angle of view is.
Focal distance is a different concept. It refers to the distance between the subject of your image and the sensor or film plane when the lens is focused on a subject. Changing the focal distance affects how much of your scene is in focus from front to back. Lenses also have a minimum focal distance, meaning your subject has to be a certain distance from the lens for it to focus at all.
Why Focal Length is Important
Focal length is an essential element in photography as this describes the angle of view or how much of a scene you can capture through the lens. Focal length also enables you to magnify subjects or make subjects appear larger within the frame.
The focal length is one of the first things you would think of when shooting images, as focal length helps determine what you can and cannot include in the frame. Consequently, focal length can alter the visual properties and context of your pictures.
Learning about focal lengths is the key to understanding how your camera and lenses can work together. In this way, you determine what your camera can focus on and how your pictures will turn out.
Focal Length Classifications
There’s a wide variety of camera lenses, and therefore, different focal lengths. From shooting broader views to capturing narrow ones, the focal length of the lens can affect an image’s overall quality. While there is no perfect focal length lens for any given situation, there are lenses with an ideal focal length depending on the type of photography you’re doing.
Prime Lens Focal Length Benefits
This is a fixed focal length lens and often has premium features. It can be wide-angle, normal, or macro. Photographers who choose lenses with a fixed focal length are looking for ultra-high image quality or very fast f-stops.
It’s not unusual to see virtually any focal length of the lens of this kind. A fisheye 8mm is a prime lens, as is a 24mm f/1.4 or 50 mm f/0.95.
Other prime lenses may be telephoto lenses such as a 500mm f/2.8 lens or a 2000mm f/11. They all have in common is superior image quality, a fast aperture or f-stop, and a very high price.
There are some modest focal length prime lenses, such as a 50 mm 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.
Zoom Lens Focal Length Benefits
Beginner photographers are often confused by zoom lenses. To many people, this focal length zoom lens is a telephoto lens, since you can “zoom in” on a subject. But in simplest terms, a focal length zoom lens can change focal lengths, while the other cannot.
This focal length zoom lens can adjust its range to be wide 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.
This focal length lens may not be telephoto at the longest focal length, but can still achieve an angle that’s wide under 50 mm of the normal lens. Zoom lenses are all different, making their focal lengths ambiguous.
Wide Angle Lenses
Wide-angle lenses have a short focal length and are generally characterized by the wider than normal angle of view or field of view, also referred to as the angle of view. At very wide lengths, the image can appear distorted and fisheye. Careful use of subject placement can eliminate or limit distortion effects.
The optical properties of focal short 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’s the focal length of wide-angle lenses? Basically, anything shorter than normal. 8mm to 35mm is considered wide on a full-frame camera.
A lens with a length of 35mm, 28mm, or even 24mm won’t look particularly wide. Shorter 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 wide angle lenses when taking portraits. For architectural and real estate photography, though, the wider field of view or angle of view may allow us to show the entire scope of a room or structure. These lenses are often used with landscape photography as well.
What’s normal, anyway? We’re not talking psychiatry here. Rather, it refers to the focal length of the human eye. By applying the definition of length to the human eye and comparing it to a lens on a 35mm camera, the result is a number in the 50 mm range.
While it’s actually more involved than that, a 50 mm lens works well as the length to give a natural perspective and field of view or angle 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 50 mm 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 lengths. Lenses included with most digital cameras have a normal length.
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While this term technically applies to a specific design of long length lenses, the term has broadened and is now essentially synonymous with any long length lens. A long, 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’s the length of these lenses? For a full-frame 35mm camera, any lens longer than the normal 50 mm range. The length of this lens can range between 85mm and 2000mm or more.
Popular lenses in this range include 85mm, 100mm, 105mm, 135mm, 200mm, or longer. Zoom are typically in the 70-200mm and 150-500mm range.
These 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 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 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 lens in the 85mm or 105mm range.
While a normal or wide 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 lens perfect for a head and shoulders portrait.
Many kit lenses will reach a length that enters portrait lens territory, but a prime lens in that 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 lenses with a shorter focal length, preferring their wider angle. With a wide lens, more of the scene can fit into the image area, and it’s easier to create an impressive depth of field.
What’s the focal length of a landscape lens? The wider the angle, the more scenery we can fit into the frame. Therefore, 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. The longer the focal length of a lens 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 50 mm, 60mm, 100mm, and occasionally 200mm. Some are even designed with a built-in flash to aid in exposure. Many lenses have a feature known as macro focusing, but very few of these lenses can focus as close as a true macro lens.
So, to avoid confusion, many manufacturers and photographers will use additional words to accurately describe the lens. We mentioned wide-angle zooms, which are commonly 16-35mm or 20-40mm.
A normal-range 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 lens, especially for crop-sensor digital cameras. This focal length 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’s the focal length of a lens all-in-one? 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 length of the lens.
How Does Focal Length Affect Perspective?
You may have heard about how focal length changes the image perspective. This is both right and wrong. While focal length doesn’t change perspective per se, it does change how you can represent the subject.
For example, your actual perspective may not necessarily be the best when shooting a scene. By positioning the camera at a particular angle, you can change the perspective and capture a different angle. Hence, perspective depends on the camera angle and how you change its position.
The focal length is an indicator of the distance between the subject, so adjusting the focal length to modify distance creates a change in perspective. Images are all framed the same; the differences in perspective only happen when you’re zooming in or moving further away from the subject.
How Does a Crop-Sensor Camera Affect Focal Length?
In this discussion, we’ve mentioned crop sensor a few times. A crop-sensor camera, as the name implies has a smaller (or cropped) sensor than its 35 mm 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 or angle 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 50 mm lens on a full-frame sensor camera will have a field of view or angle of view of 50 mm.
- A 50 mm lens on a crop-sensor camera has an apparent field of view or angle of view of 75mm, since 50 mm x 1.5 = 75mm.
In layman’s terms, your 50 mm 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 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 standard lenses 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 or angle 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 with a 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’s Focal Strength?
Some people use focal length and focal strength interchangeably. They’re related concepts but are not the same thing.
Focal strength refers to the ability of the lens to gather light and is measured in f-stops. A smaller f-stop number (e.g. f/1.8) indicates a larger aperture and a greater amount of light-gathering ability, while a larger f-stop number (e.g. f/22) indicates a smaller aperture and less light-gathering ability.
More often, photographers refer to lenses with a lot of light-gathering ability as a “fast” lens instead of a focally strong lens.
How Does Focal Length Affect 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, the longer the focal length of a length (the higher number of millimeters) the more compression causes. Compression is a phenomenon produced by lenses with a longer focal length 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 the object 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 focal 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.