Lens compression is a bit of a misnomer. It doesn’t compress anything, really—rather, it’s a type of lens distortion, like a fisheye or wide-angle lens. It affects how close or far backgrounds look in an image, even if the subject is in exactly the same spot. This video, less than three minutes long, does an excellent breakneck breakdown of how to understand lens compression:
Hosted by Pye Jirsa, the video aims to show honest, straightforward differences between Canon lenses. He grabbed seven prime lenses, placed a female model on a tree branch, and adjusted their camera placement so that she was always in the same spot of the frame.
Basically, the closer the camera is to the object, the farther away the background appears; the farther the lens, the closer together everything looks.
The easiest way to understand it is by seeing it in sequential order. The lens used is cited in the bottom-left of each image, along with the shutter speed and aperture settings:
With the 24mm lens, the tree looks like it extends a good few feet behind the model.
The background is starting to get more compressed with the 35mm…
As you can see, by the 300mm lens, it basically appears as though the tree is right next to the model. The physics of the shot have completely changed.
There’s no “better” or “worse” look, just what style you’re aiming for.
“It is a type of lens distortion. But that doesn’t mean that it’s bad. In fact, we use lens compression oftentimes to create awesome compositions that really wouldn’t be possible otherwise.” – Pye Jirsa