We've been saying for years that the term "lens compression" is misleading, but Lee Morris over at Fstoppers has put together a useful video that explains exactly why this is the case, and demonstrates it with two easy-to-understand examples.

The main issue with the term "lens compression" is that the distortion the term refers to has nothing to do with the lens itself. The issue is simply perspective distortion, caused by the distance between your camera and your subject, as well as the distance between your camera and the background.

Put another way: if your subject is 1 meter away (or feet: it doesn't really matter), and your background is 50 meters away, moving back 1 meter will double the distance between you and your subject, while barely changing the distance between you and the background—the perspective on your subject changes drastically, while the perspective on your background barely shifts at all.

 This diagram, from the FStoppers video, shows why changing your perspective appears to compress the background... When you double the distance to your subject you halve its size, but you've barely moved in relation to the background, so it remains roughly the same size in your image.

To show this concept in action, Morris uses two examples. First, he shows you how you can get the exact same perspective using a 24mm lens that you can with a 400mm lens by simply cropping the wide-angle shot. Then, he does the opposite, creating the same perspective as a 15mm shot by stitching multiple shots taken at 70mm.

Of course, that doesn't mean you should go throw out all of your lenses and just pick one focal length to either crop or stitch with. Physical limitations apply: like how much room you have to back up, how much resolution you're willing to sacrifice by cropping, and how much sanity you have to spare if you're trying to create a 15mm shot by taking a thousand shots with an 800mm lens.

The demonstration is just that: a demonstration of a concept that is often misunderstood because of the language we use to describe it. The compression you get using a long lens isn't a result of the lens, so much as the distance between your subject, your background, and the camera.