There are often discussions on photography forums about zoom lenses vs primes. Not going to get into the larger debate here. But one point that is frequently brought up by prime shooters is that you can "zoom with your feet," meaning move a little bit closer or a little bit further away to achieve the same composition as with a zoom lens. This advice is often offered to new photographers as a way to make one think about a scene and not stay rooted in one place. Taking the time to move about can force one to "see" the compositional possibilities of a scene, rather than just shooting from the first vantage point one happens to be in and flicking the zoom ring. It's good advice, don't get me wrong. But the flip side is that the composition *isn't* the same when you zoom with your feet. With focal lengths in the range of a "normal" lens it can be close, but zooming with your feet as opposed to changing focal lengths from the same shooting position are never really equal. Often it doesn't matter (which is why it is usually good advice), but sometimes it does. Wasn't feeling inspired to shoot anything interesting today, so instead shot these examples. All on a tripod with an exposure of 1/4 sec @ f/8 and ISO 200. 21mm vs 18mm vs 15mm focal length on a full frame body. Moved the tripod ~2 inches closer between lens switches, with an effort to keep the iPhone at the bottom of the frame and in the same position for each. 21mm 18mm. "Zoomed with my feet" ~2 inches forward. 15mm. "Zoomed with my feet" ~2 more inches forward. Note the widening of the background scene with the shorter focal lengths taken closer. Also notice the changes in the reflection on the iPhone as the focal length and subject distance change. "Zooming with your feet" when shooting a prime is often a good idea, especially as a learning tool to force one to not stay rooted in one spot and just flick the ring on a zoom lens. But subject distance and focal length create a certain composition and relationship between foreground and background elements. "Zooming with your feet" changes that composition/relationship. Sometimes it doesn't matter, sometimes it does.