In a nutshell
- Lens compression is a visual effect associated with telephoto lenses where the foreground and background appear closer together in an image than they do in real life
- The actual source of the effect is the relative camera distance
- Lens compression can make things in the frame seem closer or larger than they really are
Lens compression is a slippery concept. Some say it’s real; others insist it’s a myth. While it’s true the reason for the effect can be easily misunderstood, the visual impact can’t be denied. Let’s talk about lens compression, what it is and how you can use it in your own productions.
What is lens compression?
Lens compression is a visual effect associated with telephoto lenses where the foreground and background appear closer together in an image than they do in real life. The longer the lens, the more apparent this effect becomes.
It’s the opposite effect of using a wide-angle lens, which appears to extend the distance between foreground and background. In extreme cases, extension distortion can make your subject’s face appear pointier, enlarging the nose and bringing it forward while at the same time pushing the ears back. The effect can be dramatic and is usually considered unflattering.
Between these, we have neutral lenses. For instance, on a full-frame camera, a 50 mm lens is considered neutral. It will capture the scene as we see it with the naked eye. That means there will be little to no apparent lens compression or extension.
But why?
While lens compression is associated with focal length, telephoto lenses do not cause compression inherently. The actual source of the effect is the relative camera distance. Focal length only makes the distortion more or less apparent because it influences the placement of the camera and the field of view captured in the frame.
An example
Let’s say you shoot several portraits of the same person using several different focal lengths: a wide 16 mm lens, a normal 50 mm lens and a telephoto 120 mm lens. If you keep the subject and the camera at the same relative distance, changing only your lens, the subject will appear the smallest in the image captured with the 16 mm lens and the largest in the image shot at 120 mm. As mentioned earlier, the image shot at 50 mm will appear about the same as what you see in real life.
This is because the 16 mm captures a wider field of view, meaning it shows more of the landscape. This, in turn, makes your subject appear smaller in relation to the rest of the frame. At the other end of the scale, the 120 mm zooms in to capture a narrower field of view. That means your subject will take up more of the frame. Thus, the subject appears larger.
If you decide that you want your subject to appear to be the same relative size in all three images, you’ll need to move the camera. At 16 mm, the subject will need to be very close to take up the proper amount of space in the frame. Because the lens is so close, the subject will likely suffer from extension distortion, giving us the classic fisheye effect.
On the other hand, you’ll need to move the camera farther away to keep the subject from overwhelming the frame when changing from the 16 mm to the 50 mm and onto the 120 mm lens. Moving the camera back will keep the subject at the same apparent size, but what about the background?
A matter of relative distance
In this scenario, the camera is moving away from both the subject and the background. However, it’s not moving away from them at the same rate. For example, let’s say your camera is five feet away from your subject and 20 feet away from the building behind them. You want the subject to stay the same relative size when switching from the 16mm lens to the 50mm lens. To achieve this, you move the camera back to just over 15 1/2 feet from the subject. This more than triples the distance between the camera and the subject. However, that same move increases the distance between the camera and the background to 30 1/2 feet. That’s only a little over 50 percent farther.
It’s this difference in relative distance that causes lens compression. Because the background is farther away to start, its change in apparent size is less dramatic than that of the main subject. The subject gets 60 percent smaller, but the background only shrinks by 25 percent. We naturally judge distance by relative size, so the distance between the subject and the background appears to be compressed. This is especially true in the flattened world of the image. The effect is more noticeable when the subject and background are farther apart.
This is the same effect that allows tourists to take pictures that show them holding up the Tower of Pisa. (See also: Forced perspective)
And why should you care?
Knowing how and why this effect occurs will allow you to better plan and control your image. Sometimes, you may want to emphasize distance. Other times, you may want to make things seem closer than they really are. Strategic use of lens compression can also help isolate your subject in the frame, preventing background elements from distracting your viewers.
And as we just hinted at, lens compression can also be leveraged in the special effects world to make miniatures and models appear larger than life.
Lens compression in cinema
One of the most famous examples of using lens compression to support the narrative comes near the end of “The Graduate” (1967). In the scene, Benjamin Braddock is on a mad dash to stop the woman he loves from marrying another man. But time is running out. He’s running at full speed along the sidewalk toward the church where the wedding will take place, but he seems to be getting nowhere. To emphasize the distance Ben must travel and the effort he must expend to get to his destination in time, the scene is shot from a distance using a telephoto lens that provides an abundance of lens compression. This makes the sidewalk appear shorter than it really is, so it seems to take Ben an unnaturally long time to traverse that distance.
A more recent example comes from “Tinker Tailor Soldier Spy” (2011). The film includes a memorable scene, shot on a 2000 mm lens, where two characters have a conversation in front of an oncoming plane. While the plane is actually landing a safe distance away, it appears to be dangerously close thanks to the clever use of lens compression.
Lens compression can also be used more overtly to communicate a character’s internal state through techniques like the Vertigo Effect. To achieve the effect, the camera itself moves toward or away from the subject while the lens zooms simultaneously in the opposite direction. Also known as the Hitchcock shot, the Jaws effect, the Zolly or simply the Dolly Zoom, it’s a disorienting shot that gives the impression that the world is suddenly closing in on the subject.
How to achieve the best lens compression
To control the amount of lens compression that appears in your image, you’ll need to consider three factors:
- Camera-to-subject distance
- Camera-to-background distance
- Focal length
As we’ve learned, compression comes from the relationship between camera-to-subject distance and camera-to-background distance. For more compression, we want to increase the camera-to-subject distance without significantly increasing the camera-to-background distance. Since moving the camera away from the subject will not affect the camera-to-background distance as drastically, lens compression is easier to achieve when the subject is farther away from the background. To keep the subject the same relative size as we move the camera back, we’ll also need to increase the focal length.
When to use lens compression?
Lens compression is often considered desirable from an aesthetic standpoint, but you can also leverage compression for narrative impact or to achieve forced perspective effects. How you use the effect is up to you. The important thing is to understand what’s happening and why.
