In-Depth Photography Guides

The Landscape Photographers Guide to Choosing the Right Focal Length

Have you ever been confused when you hear photographers reference the settings they used to take their shots?

For example, if you were told that a photograph was taken at 14mm, what does that really mean? What about a photo taken at 70mm or 200mm?

What each of these numbers indicate is the particular focal length at which the photo was taken.

So, what is a focal length?

The simple explanation is that focal length is a physical property of a lens that determines certain attributes of an image such as depth of field and field of view.

Every lens, whether it’s a simple magnifying glass or a professional grade lens for a DSLR camera, has a has a specific focal length (or range of focal lengths).

In this article we will take a deep dive into focal length actually is at a fundamental level, how it impacts your images, and how to choose the right lens for the landscape images you want to capture.

You will learn everything from the nitty gritty fundamentals of lenses to practical information that will help you improve your skills.

When you understand what focal length means and how different focal length lenses impact your images, you will have greater creative control over the look of your images, including the depth of field and composition you are trying to achieve.

Table of Contents

Focal Length Primer: Lenses and Light Fundamentals

The focal length of a lens is a fundamental attribute of a lens that describes the light bending power of that lens.

To truly grasp focal length, it helps to have a basic understanding of what a lens is and what happens to light as it passes through a lens.

What Is a Lens?

At its most basic level,

a lens is a piece of glass or other transparent medium that bends light in a way that forms an image.

So, how does a lens bend light and how are images formed?

Light is bent by a lens through a phenomenon called refraction.

Refraction is the change in direction of light that occurs when it passes obliquely from one transparent medium from another, such as from air to water or air to glass.

A simple example that you have likely seen is a straw in a glass of water.

As figure 1 illustrates, the straw appears to be bent at the surface of the water in the glass, but we know that the straw isn’t actually bent. What is actually bending is the light as it passes through air, glass, and water at different speeds.

Refraction occurs because light slows down when it passes (obliquely) into a denser substance. Though they are all transparent substances, water is denser than air, so light traveling from air to water slows down once it meets the surface of the water.

Figure 1. A straw in a glass of water showing refraction at the water's surface that makes the straw appear bent. Credit: Sven Brandsma on Unsplash

Notice that the light in figure 1 is further bent by the glass, which is not only denser than water but also curved.

The curvature of the glass causes the light to bend at different directions as well.

Photographic lenses are comprised of one or more pieces of curved glass that bend light through refraction.

As you will see soon, the direction that light is bent is important and ultimately determines the focal length of the lens.

Simple lenses are composed of a single piece of glass and typically have two surfaces.

Each of the two surfaces is either concave, convex or flat. Simple lenses are classified by the shape of these surfaces as shown in figure 2.

What Happens When Light Passes Through a Simple Lens

Simple lenses are composed of a single piece of glass and typically have two surfaces that are symmetrical around an axis.

Each of the two surfaces is either concave, convex, or flat. Simple lenses are classified by the shape of these surfaces as shown in figure 2.

Figure 2. Different types of simple lenses. Simple lenses have two surfaces that are either concave, convex, or flat. The dotted line shows the axis of symmetry through the lenses. Each type of simple lens refracts light differently due to the variable curvatures of their surfaces.

Depending on the shape of the lens, light will either refract in a way that causes the light rays converge to a single point - the focal point - , or diverge in a way that directs light rays away from each other.

For example, biconvex and plano-convex lenses cause light rays to converge towards one another and eventually intersect at the focal point, and biconcave lenses cause light rays to diverge and scatter away from each other.

So, returning to the question: how is an image formed?

The focal point, or the point at which light rays converge, is where a sharp image is formed. Figure 3 shows how a biconvex lens refracts light rays to a single point where the image is formed.

Figure 3. Light rays (arrows) passing through a biconvex lens. These light rays are refracted by the the lens which causes them to converge to a single point (far right). This is the focal point - the point at which the image forms.

This is the point at which you want your camera's sensor, or film, or your eye to be when you want to see the image in front of you to appear in focus.

The goal of photographic lenses, as with other lenses like magnifying glasses, binoculars, and telescopes, is to converge light to a single point so that they eye, or film, or camera image sensor perceives a sharp image of what the lens is “looking” at.

For example, a magnifying glass is an example of a basic biconvex lens. When you hold a magnifying glass up to a subject that you are trying to magnify, light reflected from the subject travels toward you and the lens, passes through the lens, and converges to a single point - which is the point your subject comes into focus as perceived by your eye.

Beyond Simple Lenses

As you might imagine, modern camera lenses used for digital photography are are much more complex than simple lenses, but they work using the same principles of refraction, convergence, and divergence.

Advanced camera lenses used for DSLR’s and other sophisticated cameras are classified as compound lenses.

Instead of having one simple biconvex lens used to converge light to a focal point, compound lenses consist of a series of simple lenses aligned along an axis.

Figure 4. A compound lens is composed of a series of simple lenses aligned along an axis. Source: Wikipedia

Each simple lens in the series is called an “element” of the camera lens. Most photographic lenses have somewhere between 4-9 glass elements. Elements can also be joined together into groups.

When light enters and passes through the barrel of a camera lens, it proceeds through a series of these glass elements, each with differing refraction and dispersion properties.

Each of these lens elements is specially shaped to bend light in a way that either converges or diverges it as it passes through the lens barrel.

At the end of its journey through the lens barrel, light ultimately converges to a single point near the camera’s image sensor.

Like with simple lenses, this point is where the image is formed. With compound lenses, however, light has to travel through several more simple lenses, or elements, before it converges to form an image.

Compound lenses, especially professional grade ones, produce much higher resolution and detail in the images that they produce on film and image sensors.

The series of elements inside these lenses are engineered to reduce optical defects called aberrations which degrade the sharpness and quality of an image.

What is Focal Length?

Once you've learned the basics of how lenses work, this next section will help you understand what focal length means at a technical level.

The focal length of a simple lens is the distance between the lens and the point where light rays converge to form a sharply focused image of an object when the lens is focused at infinity. This distance is measured in millimeters (mm).
  • Note: focusing to infinity, in practice, just means that the lens is focused on something on the distant horizon, such as a mountain in the distant background of a scene.

Figure 5 below illustrates how focal length is measured for a simple biconvex lens. As light (red arrows) passes through the lens, it is refracted in a way that causes the light rays to converge towards one another. These light rays intersect at the focal point - the point at which light focuses and forms an image. The distance between the center (vertical axis) of the lens and the focal point, is the focal length.

Figure 5. Illustration of how focal length is measured for a simple lens. Light rays (shown as red arrows) pass through a biconvex lens and converge to form an image. The distance between the lens and the point of focus is the focal length.

In a compound lens use for photography, the definition of focal length is slightly more complex.

Technically, the focal length of a compound lens is the distance between the lens’s rear nodal point and the camera’s sensor or film when the lens is focused at infinity.
  • Note: a nodal point is one of three pairs of “cardinal” points within an optical system, such as a compound camera lens. A geeky discussion of the physics of what a nodal point is is beyond the  scope of this article, but if you interested you can learn more about these points and how they work here. It can be useful to think of this point as the optical center of a lens.

Figure 6 illustrates the behavior of light as it passes through a compound camera lens and how focal length is measured within this type of optical system. Note that focal length is the distance, measured in millimeters (mmm) between the rear nodal point (i.e. "optical center") of the lens and the image sensor of the camera.

Figure 6. Illustration of how light (red arrows) behaves inside a compound camera lens. The distance, measured in millimeters (mm) between the rear node/optical center of the lens and the image sensor (or film plane).

If this is at all confusing, don't worry too much about it. You don't need to understand the physics.

The most important thing to take away here is that the focal length of a lens is a quantifiable property of how light behaves in a lens that is measured in millimeters.

How to Find the Focal Length of Your Lens

The focal length of a lens is typically displayed on the outside of a lens.

It can be displayed as either a range of focal lengths (e.g. if it is a zoom lens), showing the minimum and maximum in the case of zoom lenses (such as the lens in Figure 7), or will be a single number as in the case with prime lenses (fixed focal length lenses).

Figure 7. A lens with a focal length of 70-300mm. Focal lengths are typically displayed on the outside of a lens.

How Focal Length Impacts Field of View (FOV)

You  are likely already aware that some lenses can magnify a subject more than others.

For example, consider how much stronger the magnifying power of a telescope is compared to that of a simple magnifying glass.

The reason why two very different lenses can magnify the same scene to such different degrees comes down to the differences in their focal lengths.

  • the shorter the focal length, the less magnified your subject will be
  • the longer the focal length, the more magnified your subject will be

It follows that the more magnified your subject is, the less of the entire scene will fit into your frame due to the fact that your subject will take up a larger proportion of the image.

This is shown in Figure 9 below. Notice how the red barn is more magnified as the focal length gets longer. Also, notice how less of the entire scene is captured at the longer focal lengths compared to shorter ones.

Figure 9. A series of photographs taken of the same subject at different focal lengths. Source: Nikon

The amount of the scene you can see through the viewfinder is called the field of view (FOV). Thus, Figure 9 shows a progressively smaller FOV as focal length increases. This is further illustrated in Figure 10, below.

  • Note: Field of view is often used interchangeably with the term angle of view (AOV), which describes the angular amount the scene captured by the lens, described in angular degrees.
Figure 10. A comparison of the angle of view produced at different focal lengths. Focal lengths are categorized into wide, standard, and telephoto lenses based on their focal lengths. This is explained in the next section.

In summary, here’s what you need to understand about FOV as it relates to focal length:

  • the shorter the focal length, the less magnified the image, the wider the FOV
  • the longer the focal length, the more magnified the image, the narrower the FOV

How Focal Length Affects Depth of Field

Depth of Field (DOF) is the distance between the closest and farthest object in a photo, both of which are acceptably sharp.

In other words, DOF refers to how much of your image is in focus.

A shallow DOF means that a relatively small part of your image is in focus, and a deep DOF means that a relatively large part of your image is in focus.

For a more in-depth explanation of DOF, check out my complete guide to f-stop and depth of field.

The focal length of the lens you choose will be a factor that affects the DOF of your images.

Focal length has the following inverse relationship with DOF:

  • the shorter the focal length, the deeper the DOF
  • the longer the focal length, the shallower the DOF

This relationship between focal length and DOF tells us that our 14mm wide angle will have a deeper DOF relative to our 200mm telephoto lens, which will have a shallower DOF.

Note: you won’t see much of a change in DOF between different lens focal lengths until you get into much higher focal lengths, usually in the upper telephoto focal lengths greater than 100mm.

How Lenses are Categorized by Focal Length

Lenses are typically grouped into the following general categories defined by focal length.

  • wide-angle: 35mm or less
  • standard: 35mm-70mm
  • telephoto: 70mm and above

Certain genres of photography tend to be dominated by certain focal length ranges, as these ranges are often ideal of the types of images these photographers produce.

Table 1 below summarizes of some of the major photography genres and the focal length ranges that are most often used in them.

Table 1. The main categories that lenses are grouped into based on their focal lengths.

Wide-angle Lenses (<35mm)

Wide-angle lenses include all lenses that have a focal length of 35mm or less.

These lenses capture a wide FOV and deep DOF compared to lenses with focal lengths above 35mm.

Because of these two main attributes, landscape photographers often use wide-angle lenses with short focal lengths when they are trying to capture a large, expansive scene.

These short focal length lenses are ideal for shots where you want to get everything in the foreground and the background, such as a flower a few feet away and a mountain in the distance, to fit in in a single image, as shown in Figure 11 below.

Landscape photograph of mountain and purple flowers
Figure 11. A photograph shot with a wide-angle lens. Note the wide depth of field and large field of view. Source: Ales Krivec on Unsplash

Not only will more of the scene be capture, but more will be in focus because of the deeper DOF you can get, especially if you set the focus point appropriately (e.g. near or at the hyperfocal distance).

However, a caveat to using wide-angle lenses in landscape photography is that your subject in the background, such as a mountain, will look much more distant in the image than it actually appears to your eyes in real life.

If your main subject is at the back of your composition or at the horizon, it will be small and likely unimpressive compared to what it looks like when viewing it with the naked eye.

For example, in figure 9 above, the red barns appear much more distant and smaller when shot at 18mm than it is at 55mm (a focal length close to what we see in person). Even though a large amount of the scene is captured, the subject looks unimpressive and uninteresting.

Also, wide-angle lenses, especially ones at very small focal lengths (e.g. ultra wide-angle), can make objects near the margins of the image look stretched.

This type of distortion is called barrel distortion because it makes the image appear as if it is wrapped around a barrel.

In barrel distortion, magnification of the image decreases with distance toward the edges of the frame, which will make the photo look warped along the gridlines shown in Figure 12.

Figure 12. Gridlines showing the lines along which an image can be warped due to barrel distortion. Source: Wikipedia

This occurs because wide-angle lenses are designed to squeeze a wide-angle of reflected light from a scene onto an image sensor. Bending light to such a large degree causes the image to literally look bent.

The amount of barrel distortion a lens produces varies.

Although barrel distortion is most apparent in lenses with short focal lengths, it can also be seen to lesser degrees when using lens with focal lengths longer than the wide-angle range.

For a zoom lens that has a range of focal lengths, you will start to see barrel distortion show up around the middle of the lens’s focal length range, and it will be the most apparent at the smallest end of the range.

The amount of barrel distortion of a lens is also dependent on on how close the subject is to the camera. The closer you are to your subject, the more barrel distortion you will see.

Once you get to about 24mm and above, barrel distortion becomes less apparent, which is something to keep in mind when choosing a focal length.

As a landscape photographer, barrel distortion is something to consider when using wide-angle lenses as it could potentially make objects near the edges of your image look like they are leaning in toward the center of the image, such as a tree or a person.  

You will often see less of this aberration with high-end, professional lenses, which use additional lens elements to compensate for the distortion. This not only makes them much more expensive, but heavier, too.

Standard Lenses (35mm-70mm)

Standard lenses include all lenses that have a focal length between 35mm and 70mm.

These lenses produce images that have the closest FOV to what we see directly with our eyes, which makes them great for everyday types of photography of humans and pets.

The human eye has an angle of view of about 40-60° (not including peripheral vision) which corresponds to a focal length of about 35-50mm.

A 50mm camera lens is about the closest to a normal human FOV that will produce an image comparable to what you see with your eyes naturally, minus peripheral vision.

These lenses have the least amount of distortion, which makes them practical for everything from portraits and product photography, to street and journalistic photography.

The DOF produced by these lenses will generally get smaller as focal length increases, provided that aperture and subject distance are kept the same.

Telephoto Lenses (35mm-70mm)

Telephoto lenses include all lenses that have a focal length above 70mm. Lenses within this range that have focal lengths above 300mm are usually called super telephoto lenses.

They have a narrow FOV and a relatively shallow DOF.

These lenses also have a high magnification power and are ideal to use when you can’t get close to your subject.

This makes them great for wildlife photography where it is usually unsafe for or impractical to get close to an animal. They are also very useful when you want to capture a subject in the distance, such as a mountain or water feature, up close in a way that makes it more dominant in your composition.

There are several important things that you should take into consideration when using telephoto lenses.

1. The first is that one you start getting above 100mm in focal length, you will really start noticing a decrease in DOF.

This will make it more difficult to get the majority of your composition in focus, and you might find that you are needing to increase your f-stop value and/or move further away from your subject in order to compensate for this.

It does, however, give you the opportunity to get more creative and experiment with isolating and drawing the eye to your subject by softening the foreground and background out of focus. An example of this is shown in Figure 13 below.

Photo of deer in the woods
Figure 13. Telephoto lenses, which are the typically used by wildlife photographers, have a relatively shallow depth of field. Here the subject, a young buck, is in focus, while the foreground and background are out of focus. Source: Casey Horner on Unsplash

2. Second, images taken with telephoto lenses tend to look more flat or “compressed,” where the background looks closer to the subject than it actually is.

This compression effect occurs because you have to be further away from your subject when using a telephoto lens to capture it within the perimeter of your frame.

In other words, due to the magnification power of these lenses, you have to be much further from your subject when using a telephoto lens in order to get the same composition as you would with a wide angle or standard lens.

When you get further from your subject, the ratio of the distance between you and the subject and you and the background gets smaller. This diminishing ration is essentially what results in an image appearing more compressed.

3. Telephoto lenses are typically heavier than lenses with shorter focal lengths, and the added weight can really be burdensome for a landscape photographer who hikes or backpacks with their photography gear.

The extra weight might be impractical for long hikes or trips, especially when you are gaining lots of elevation hiking up mountains, like we do a lot of here in Colorado.

4. A final consideration you should take when shooting at higher focal lengths is the fact that it is much easier to introduce motion blur into your images due to camera shake - something that occurs when the lens isn’t held still enough for the entire exposure.

There are a few reasons camera shake becomes a problem at higher focal length, which include:

  • Heavier lenses are harder to hold still.
  • They are typically used to take photos of a subject from a distance. Slight movements of the camera will equate to much larger movements of your subject within the frame when viewed from far away.

In order to avoid camera shake, you will want to make sure that your shutter speed is fast enough to compensate for the movement that naturally occurs when hand holding a lens.

As a general rule, you can get away with hand holding a lens by setting the shutter speed to equal the reciprocal of the focal length (1 over the focal length). For example, if you are using a 200mm lens, set your shutter speed to 1/200 S or faster.

If you are in a low light situation where you can’t slow down your shutter speed enough to get a proper exposure, you will want to use a tripod to keep the camera as steady as possible.

Alternatively, some lenses come with a feature called Vibration Reduction (VR) or Image Stabilization (IS), which is a great option that will allow you to decrease your shutter speed up to a few exposure stops.

  • Note: you will want to turn this feature off when shooting with a tripod, as you can actually introduce more motion blur by using VR or IS with a tripod.

How to Choose the Right Focal Length

The lens you decide to use for an image really comes down to the composition you are trying to create and the creative elements you want to incorporate into your image.

It is important to think about the intention behind the image you are trying to create before choosing a lens of a particular focal length.

Ask yourself what message or story you are trying to tell, or the emotion you are trying to convey.

Think about the elements of good composition and how to frame your subject in a way that accomplishes your creative goals.

Are you trying to capture a grand vista with a wide FOV or an intimate portrait of a mountain peak within a narrow FOV? How much of the frame do you want your subject to occupy? Where do you want the viewers eye to go? How much DOF is necessary to accomplish your goals for the image?

The answers to these questions will largely determine what lens you choose, and there is really no right or wrong answer to any of them.

Focal Length and Composition

Composition can change drastically and from one focal length range to another, and a photo that is powerful when taken with a telephoto lens can look uninteresting or dull with a wide-angle lens.

For example, in figure 9 above, the red barns appear very distant and small when shot at 18mm. Even though a large amount of the scene is captured and the viewer gets a lens of place, the subject looks unimpressive and uninteresting.

On the other hand, when this scene is shot at 135mm or 200mm, I would argue that the composition is more interesting. Not only does the composition follows he Rule of Thirds, but the subject is a lot more obvious as well due to the fact that the FOV is reduced and it takes up more of the frame.

Therefore, it is very important to consider the focal length you choose when determining how you want to capture a particular scene and the composition you are trying to make.

Now, if the photographer who took the images in figure 9 wanted to use an 18mm lens to get the same composition that was taken with a 200mm, she would have to walk much closer to the subject to achieve this.

It is important to understand that if you are are able to step closer to your subject, you could potentially get the same FOV and similar composition using a wide-angle lens than you would if you were further away from your subject and using a telephoto lens.

Doing so would likely increase the barrel distortion introduced from using a wide-angle lens, but it would also increase depth of field, making it easier to get most of the image in focus.

This works the opposite way, too.

If you step away from your subject, you could get your subject to fill the same proportion of the frame (i.e. similar FOV and composition) using a telephoto lens as you would if you were up close using a wide-angle lens.

However, the impact of this on your image would be that the DOF would be reduced and it would be harder to get the entire image in focus. It would also cause motion blur to become an issue, among other things.

It is really your creative intention behind the image and the compromises you are willing to make that will determine which focal length works best for the composition you are trying to create.

Effective Focal Length: Image Sensors and Crop Factors

There is one final but very important piece of information that you should be aware of and understand when it comes to choosing a lens or particular focal length.

The concepts and principles you have learned throughout this article apply to full frame DSLR or mirrorless cameras which have a sensor size equivalent to a frame of 35mm film (measuring 36mm x 24mm).

However, cameras that have smaller image sensors, or “cropped” sensors, will produce images that have a reduced the FOV and DOF when shot with full frame lenses.

This will cause images to appear as if they were taken with longer focal length lenses when compared to images taken with the same lenses on a full frame camera.

In other words, cameras with cropped sensors create photographs that are more magnified (i.e. zoomed in) relative to images produced by cameras with full frame sensors, as if they were shot with longer focal length lenses.

This “new” focal length is called the effective focal length, and it can be found with a simple calculation (see next section below).

Once you calculate the effective focal length, to visualize what the FOV will look like when compared to a 35mm film or full-frame camera.

Note: effective focal length is different than the actual focal length, which is a physical property of the lens. It is a term that refers of how a lens behaves when shot on a cropped format camera compared to a full frame one.

The effective focal length is calculated by multiplying the focal length of a full frame lens by a number called a crop factor, or focal length multiplier, which is will be specific to the size of the crop sensor you are using.

Technically, the crop factor is the ratio of the cropped sensor size to the size of a 35mm frame or full frame sensor.

While cropped sensors come in a variety of sizes a common cropped sensor format you will likely come across are APS-C format cameras.

These have a crop factor of 1.5 (for Cannon) and  1.6 (all other camera manufacturers including Nikon, Sony, Fuji, etc.)

How to calculate the Effective Focal Length

Here is how to calculate the EFF:

EFL = lens focal length x crop factor

Lets say you have a 35mm full frame lens that you want to use on an APS-C format Nikon camera.

To get the EFL, you would multiply 35 x 1.6, which equals 56.

This means that your 35mm lens will behave like a 56mm lens on your cropped sensor APS-C format camera.

The images you take will be more magnified and the FOV will be reduced compared images taken with this lens on a full frame camera.

Summary

  • The focal length of a lens is a fundamental attribute of a lens that describes the light bending power of that lens.
  • At its most basic level, a lens is a piece of glass or other transparent medium that bends light in a way that forms an image.
  • Simple lenses are composed of a single piece of glass and typically have two surfaces that are symmetrical around an axis.
  • Depending on the shape of the lens, light will either refract in a way that causes the light rays converge to a single point - the focal point - , or diverge in a way that directs light rays away from each other.
  • The point at which light rays converge is where a sharp image is formed.
  • The focal length of a simple lens is the distance between the lens and the point where light rays converge to form a sharply focused image of an object when the lens is focused at infinity. This distance is measured in millimeters (mm).
  • The focal length of a compound lens is the distance between the lens’s rear nodal point and the camera’s sensor or film when the lens is focused at infinity.
  • The focal length of a lens is typically displayed on the outside of a lens.
  • Lenses can have a single focal length or a range of focal lengths. Lenses with a single focal length are called prime lenses, and lenses with a range of focal lengths are called zoom lenses.
  • The shorter the focal length of a lens, the wider the field of view (FOV), and the longer the focal length, the narrower the FOV.
  • FOV refers to the amount of a scene you can see through the camera’s viewfinder.
  • The shorter the focal length of a lens, the wider the depth of field (DOF), and the longer the focal length, the shallower the DOF.
  • Lenses are typically grouped into three general categories defined by focal length. These include wide-angle (35mm or less), standard (35mm-70mm), and telephoto (70mm and above) lenses.
  • Choose a lens based on the composition you want to create and the creative intention behind your image.
  • Cameras that have smaller image sensors, or “cropped” sensors, will produce images that have a reduced the FOV and DOF when shot with full frame lenses.
  • This results in an effective focal length that can be calculated by multiplying a lens’s focal length by the the image sensor’s crop factor.

Zoom vs. Prime Lenses

Lenses can have a single focal length or a range of focal lengths.

The lens shown in Figure 7 (above) shows a zoom lens that has a a range of focal lengths between 70-300mm. This means that the photographer can choose any focal length between 70-300mm simply by adjusting the focal length ring. As you will learn soon, adjusting the focal length with impact the look of your image in several ways.

Prime lenses, on the other hand, have a single, fixed focal length. While this makes them less versatile than zoom lenses, the do typically have better resolution and produce sharper images.

You can learn more about the pros and cons of of zoom vs. prime lenses here.

How to Find the Focal Length of Your Lens

The focal length of a lens is typically displayed on the outside of a lens, as shown in Figure 7.

Zoom lenses display a range of focal lengths, which are the minimum and maximum focal lengths available on the lens.

Prime lenses display a single focal length, as these lenses have one fixed focal length.