When zone focusing, you’re taking advantage of the hyperfocal distance of your lens. This simply refers to the focusing distance that gives your photos the greatest depth of field and gets both the foreground and the background sharply focused. The hyperfocal distance depends on the aperture and the focal length of your lens. In older manual focus lenses, you can see this in the form of the depth of field scale (if your lens has it, find out how you can zone focus with it here).
Another term you’ve probably heard of is “f/8 and be there” which is a simple summary of the hyperfocal focusing technique. This means you can pretty much get everything in focus if you set your aperture at f/8 and set your lens or camera’s focus a few meters away. With smaller apertures, objects further away continue to be sharp even if you focus your lens more closely. You can start off with f/5.6, but this technique yields sharper focus throughout your frame with either f/8 or f/11.
Surely, after reading about all the technicalities, you now want to see it work in an actual street photography session. Mark Wallace demonstrates how fast you can go when you’re using hyperfocal focusing in the video below:
Want to learn more about hyperfocal focusing? Mark Wallace also discusses this in detail in this other video.