Focal Length and Field of View Explained in 4 Steps
- With a wider view, you are required to get closer to your subject if you want to fill the frame. If you don’t, there will be more background included in the shot.
- Wide-angle lenses have the appearance of more depth of field - that is, the area of the image that’s in sharp focus - than longer focal length lenses. As a result, the background (which, as noted above, there is more of) is more in focus).
Lens Field Of View
Just like our eyes are our windows to the outer world, lenses are the eyes of the camera to the outer world.
And just like each person has different eyes with different capabilities, so too do lenses.
That means that what one person sees, another might not see the same scene in the same way. The same goes for lenses.
Some lenses have a short focal length, and therefore a very wide angle of view; others have a very long focal length, and therefore a narrow angle of view.
But what exactly does all that mean?
Let’s review these concepts in more detail.
Focal Length is Important, But Field of View is More Important
Focal length tells us how long a lens is. Naturally, that’s important information for photographers.
However, field of view is more important.
It’s simple: field of view informs us as to how much of a scene a lens can see. In other words, it’s a more informative benchmark regarding what you can photograph with the specific camera and lens you’re using.
This is important to note: field of view changes as two factors change - focal length of the lens and the size of the sensor (or size of film) your camera uses.
The difficulty is that field of view, though it’s more informative, changes depending on the size of the camera’s sensor. As a result, focal length, which does not change, is what’s most commonly used by camera manufacturers. In the video below, Larry Becker of B&H Photo addresses the concepts of camera sensors and crop factor, and how they can be used to determine the field of view.
Here’s an example of how to determine a lens’s field of view:
On a full frame camera, a 50mm fixed lens has a 47-degree field of view. That 47-degree field of view is roughly what we see with our own eyes.
But, put on a crop sensor camera, that same 50mm lens has a different field of view. Now, there are different levels of crop, but assuming the camera has a crop factor of 1.6x, the field of view lessens to about 30-degrees.
This is an important distinction because with that narrower field of view, you’d have to move further away from your subject to capture an image that’s roughly similar to one captured with the same lens on a full frame camera.
Of course, you could also use a different lens.
Where a 50mm fixed lens has a 47-degree field of view on a full frame camera, a 31mm lens has a 47-degree field of view on a 1.6x crop sensor camera. Unfortunately, no one makes a lens at that focal length, so you’d have to approximate with something slightly shorter or longer, say a 35mm lens.
Looking at the chart above, you can see the various focal lengths on full frame, crop sensor, and micro four-thirds camera systems that achieve the same field of view. For example, a 20mm lens on a full frame camera, a 13mm lens on a 1.6x crop sensor camera, and a 10mm lens on a micro four-thirds camera all have a field of view of 94-degrees.
Note as well how the field of view narrows as the focal length increases. At the bottom of the chart, a 400mm lens on a full frame camera, a 250mm lens on a 1.6x crop sensor camera, and a 200mm lens on a micro four-thirds camera only have a 6-degree field of view.
So, with all those technicalities out of the way, what impact does this have on your ability to compose a photo?
If You Want to Include More of the Scene, Go Wide-Angle
A wide-angle lens has the widest field of view at about 63-degrees. But, as noted above, the field of view depends on the size of the camera’s sensor.
So, on a full frame camera, a lens that’s 35mm or shorter is considered wide-angle, where approximately 20mm and smaller is considered wide-angle on a crop sensor camera. If you shoot with a micro four-thirds, you’d need to go to around 18mm to reach a wide-angle field of view.
From a compositional standpoint, there are two things to consider with a wide-angle lens:
That means that when you’re shooting wide-angle, you will incorporate more of the scene into the shot than if you used a longer lens. Because of this, landscape photographers tend to like wide-angle lenses because they can incorporate more of the scene from left to right and more of the scene from foreground to background into the shot while maintaining sharp focus.
This concept can be seen in the beach image above. Note how you have a full view from left to right and how everything from the foreground to background is in focus.
Additionally, wide-angle lenses offer an interesting perspective in that they create images with a lot of depth. This is a feature that longer lenses tend to lack, especially telephoto lenses.
Normal Lenses Offer a Compromise
For a slightly narrower field of view, normal lenses are the way to go.
At approximately 55-degrees, these lenses have a wide enough angle of view to incorporate much of the scene into the image, but it’s also narrow enough that the image doesn’t quite achieve the same depth and dimension as is possible with a wide-angle lens.
Having said that, a normal lens offers a wider angle of view than a telephoto. You can incorporate much more background than you can with a telephoto, but because normal lenses tend to have very large maximum apertures, you can easily blur the background to bring more attention to your subject. In the video above, watch as Tony and Chelsea Northrup offer an overview of this concept and explore how you can use field of view and depth of field to compose improved portraits.
If You Want to Restrict What’s in the Scene, Go Telephoto
Like wide-angle and normal lenses, the field of view for telephoto lenses changes with the type of camera. On a full frame camera, an 85mm lens is considered telephoto, where a 50mm lens is considered telephoto on a crop sensor camera. A micro four-thirds camera requires just a 40mm lens to produce telephoto results.
Each of these lens/camera combinations produces a field of view of around 30-degrees. Compared to the wide-angle field of view of 63-degrees, you can see how much more restrictive telephoto lenses are.
As a result, telephoto lenses are used to create more intimate shots. You can more easily fill the frame with your subject and exclude elements of the scene that don’t fit or are unwanted. You can create images with little ancillary detail, both from a lateral perspective and a depth perspective.
Looking at the image above, you can see just how much of the surrounding environment can be omitted from a shot when using a telephoto lens. Where a wide-angle shot of the same scene would have likely incorporated the entirety of the Golden Gate Bridge, with a telephoto, the scene is vastly restricted, allowing the photographer to focus our attention on just a few elements - the single bridge tower, the city skyline, and the fireworks.
Wrapping It Up
In short, field of view is an important factor to bear in mind because it will help determine the look and feel of your shot. For a lot of depth and dimension, go wide-angle. For a narrower, more intimate shot, go telephoto. For something in between, choose a normal length lens.
But, bear in mind the type of camera you use, and utilize the chart included in this lesson to determine what field of view your particular lens will generate on your camera body. Then you can match your lens to your subject to achieve better results.
Though it’s certainly a bit confusing at first, the more you work with focal length and field of view, the easier it will be to understand - and to use to your advantage to take improved photos.