Sometimes autofocus can be really annoying: it’ll search and search for an object to focus on, and either never find it, or go through multiple cycles until it finally finds the right object to focus on. And by that time, you may have already missed the shot–especially if you’re photographing a quick moving subject like birds.
The switch (pictured above on my Canon 300mm f/4L lens) basically tells the lens where you’ll be focusing: either on a near object or a far object. It limits the range of where your autofocus will search.
So, with the switch turned to 3m or beyond, my lens won’t try to focus on anything closer than 3 meters. This makes the autofocus work a lot faster when I know I’ll be focusing on something far (like wildlife). It’s a good idea to get in the habit of checking this switch before you get into “wildlife photography mode”
This little switch may not be available on all lenses (it really only makes sense on long telephotos), but check your lens and manual to be sure. I did a quick search for Nikon lenses and found out a similar switch is available on their longer lenses, it’s just called something different: focus limit switch (you can set it to “LIMIT” or “FULL” where the “LIMIT” setting will only try to focus on far objects).
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About the Author: Steve Berardi is a naturalist, photographer, computer scientist, and founder of PhotoNaturalist. You can usually find him hiking in the beautiful mountains and deserts of Southern California.