Focal Length: 10 Important In-Depth Tips at Using and Understanding Camera Lenses

Focal Length Highlights: Wide-angle lenses can create a very intimate feeling, whereas telephoto lenses magnify your subject and create blurred backgrounds.

Picking a focal length for each scene you shoot is a significant creative decision. It defines how much of the scene is captured in the shot, how tight the audience feels to the subjects, and how much background blur you can accomplish. 

Choosing the proper focal length for your lens is just as important as deciding on the quality of light and color grading you want with the look and feel of your work. Don’t worry if this seems a little overwhelming: here’s your focal length explanation.

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Focal Length: An In-Depth Look at Using and Understanding Camera Lenses

What exactly is focal length?

The focal length of your lens is the distance between the optical center (where light rays converge) and the sensor or film in your camera.

The focal length of a lens is measured in millimeters, and the higher the number, the longer the lens. (This may seem obvious, but given how aperture works, it bears repeating.)

Focal Length: An In-Depth Look at Using and Understanding Camera Lenses

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Photo lenses with a focal length and angle. 

  1. ultra-wide 
  2. wide-angle 
  3. normal 
  4. short telephoto (70-85mm) / medium telephoto (100-200mm) 
  5. super-telephoto (300-400mm) / ultra telephoto (500-1200mm)

The longer your lens, the narrower your angle of view, which means less of the scene will be captured, but your subject will appear larger. 

Prime lenses, for example, have fixed focal lengths of 35mm or 50mm. Zoom lenses, on the other hand, can cover a wide range of focal lengths, such as 18-35mm or 70-200mm.

Focal Length: An In-Depth Look at Using and Understanding Camera Lenses

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Don’t mix up the focal length and focal distance. The focal distance is the distance between your subject and your lens. Every lens has a minimum focusing distance, which determines how close you can get to a subject before your lens loses focus.

The angle of view and field of view

When it comes to focal length, you’ll hear people talk about “angle of view” and “field of view.” They aren’t exactly the same thing, but they are very similar, and as a result, they are frequently used interchangeably.

They both refer to how much your lens can “see.” The field of view refers to how much of your scene can be captured in a single shot. Consider the horizontal distance that your lens can capture from left to right.

The angle of view is a precise measurement in degrees of what your lens can “see.” A wide-angle lens, as the name suggests, has a wider field of view than a telephoto lens.

A 50mm lens on a 35mm sensor will have a 39.6-degree angle of view; a 24mm focal length will have a 73.7-degree angle of view, and a 200mm focal length will have a 10.3-degree angle of view.

Sensors for full-frame and crop

When we talk about lens focal length, we usually assume that the lens will be used with a full-frame, 35mm sensor.

However, if your camera has a crop frame sensor, using a 50mm lens on it will not provide the same angle of view as using a 50mm lens on a 35mm sensor. As a result, the smaller sensor effectively increases the focal length while decreasing the angle of view.

If you’re using a crop frame sensor camera, you can calculate the equivalent focal length of a lens by multiplying it by the crop factor of your sensor.

Canon APS-C sensors, for example, have a crop factor of 1.6. As a result, a 50mm lens has an equivalent focal length of 80mm.

Many lenses designed specifically for mirrorless cameras will be sold with their actual focal lengths listed alongside the 35mm equivalent.

Wide-angle lenses

Wide-angle lenses have focal lengths that are shorter than the diagonal measurement of the sensor on your camera. They typically range in size from 23 to 35mm. A lens with a focal length less than 23mm is referred to as an ultra-wide-angle lens.

Normal or common lenses

Normal lenses are so-called because they are thought to be the most similar to how the human eye sees the world. A normal length lens’ focal length calculation is anything similar to the diagonal measurement of your camera’s sensor.

That’s 43mm on a 35mm sensor. A normal (or standard) lens has a focal length of 35 to 70mm.

Telephoto zoom lenses

A telephoto lens has a focal length greater than 70mm, which is why they are also referred to as long lenses.

Exaggeration

Wide-angle lenses exaggerate a scene’s sense of space. They will make it appear as if subjects are further apart than they are, emphasizing the depth of a scene.

Wide-angle lenses also magnify sizes: small objects in the background appear smaller than usual, while larger objects in the foreground appear unnaturally large. When you film someone up close with a wide-angle lens, their nose and chin will appear comically oversized.

Use a wide-angle lens if you have a small room and want to make it appear larger.

By bringing a wide-angle lens close to your characters, you can instill a sense of intimacy in your audience without making them appear too large. Rather than being passive observers, the audience will feel as if they are a part of the action.

Compression

Whereas wide-angle lenses can exaggerate a scene’s sense of space, telephoto lenses do the opposite: they compress it. Telephoto lenses make the background appear closer to the subjects or objects in the scene than it is, effectively flattening it.

They can also depict characters as being much closer to one another, emphasizing their intimacy. Background subjects can appear to be roughly the same size as those in the foreground.

A wide-angle lens, on the other hand, can bring the audience closer to the subjects, whereas a telephoto lens can do so from a distance. This can give the audience the impression that they are mere observers or even voyeurs.

Telephoto lenses are often thought to “have” a shallower depth of field than wider lenses. This isn’t entirely correct. Telephoto lenses magnify the subject in the scene, making the background appear more blurred and resulting in a shallow depth of field.

Changes in movement and focal length

Use a wide-angle lens to increase the perceived speed of someone or something moving toward or away from the camera.

A car speeding toward the camera, for example, will have the audience on the edge of their seats if filmed with a wide-angle lens. Use a telephoto lens to get a better sense of the speed of a person or object moving across the screen.

If you intend to use a tracking shot in a scene, the focal length you choose, as well as the speed and direction of movement, will affect how it feels. If you’re not sure, try it!

Which is better, a prime lens or a zoom lens?

Both prime and zoom lenses have advantages and disadvantages. The most significant advantage of a zoom lens is the versatility it provides in terms of focal lengths. 

However, prime lenses are typically sharper and have wider apertures, which can be very useful when shooting in low light or natural light situations so that you don’t have to select a camera ISO that is too high.

Related Article: 5+ Best Reasons Why A Filmmaker Needs A 50mm Lens | Nifty Fifty Prime Lens

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Conclusion - What focal length should I use? 

There is no correct or incorrect answer to this question.

The focal length you should use is determined by how close you want the audience to feel to the characters, how close you want the subjects to appear to each other, how you want the background to appear, and how much of a sense of movement you want to convey. 

You can have as much space as you want in a scene. Furthermore, how you see the world influences many of your focal length choices. Do you prefer to focus on the big picture or the finer points? These preferences may also influence your lens selection. 

This is how focal length is explained.

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About the author: Trent (IMDB Youtubehas spent 10+ years working on an assortment of film and television projects. He writes about his experiences to help (and amuse) others. If he’s not working, he’s either traveling, reading or writing about travel/film, or planning travel/film projects.

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