Autofocus Versus Manual Focus

Pan
Pan

If you’re anything like me — which, for the purposes of this post, means you’re just about blind as a bat without your glasses — autofocus can be a godsend. It’s pretty useful for a host of other reasons and situations as well. Shooting sports or animals, shooting from the hip, shooting at odd angles… there are times that it’s a good thing that the camera can take care of at least one variable for you, and generally do it pretty reliably. There are times, however, when AF isn’t all that it’s cracked up to be, and you need to eyeball your shot for the best results.

  • Shallow DOF (Depth of Field): This comes into play in two situations. One is when you’re using a lens wide open (say, in the 1.4-3.5 range), either to let in more light or to blur your background. The other is when you’re using a long lens. Someone who knows the physics of these things could probably explain far better than I could, but for whatever reason, a lens racked to 300mm at f/8 acts very much like a 50mm at f/1.8. In either case, your focal plane (the part of the photo that’s in focus) can be razor thin. While autofocus will pick something to focus on, the camera’s idea of what should be in focus may not be the same as yours.
  • Low Contrast/Lousy Lighting: Whether your camera uses contrast detection or phase detection for autofocus, both systems require varying degrees of contrast in order to work well (there’s a better explanation here). Bottom line: if there’s not much contrast (your subject’s color and lighting is similar to its background, for instance) or if you’re working in low light, your camera’s AF may “hunt” for a focal point.
  • Stealth: In low light (where your AF assist light is likely to go off) or if you’re using older, screw-drive AF lenses (which are cheaper than their newer counterparts, but can also be noisy), you may inadvertently draw attention to yourself at a time when you’re trying to stay incognito.
  • Deer Photobomb

    “Busy,” Cluttered, or Active Scenes: I usually love my camera’s AF system, but there are times that it works a little too well. I had initially tried a couple of shots of the deer in Figure 2 using autofocus, only to find that the little AF point in my viewfinder kept skittering between blades of tallĀ grass rather than locking on the deer, where I wanted it. Similarly, if you’re trying to shoot through a chain link fence or a window (especially if the window’s dirty, or if there are reflections you’d rather didn’t distract from the subject), you may find that the AF keeps wanting to focus on what’s closer.

  • Portraits: If you’re filling the frame with your subject’s face (and, for that matter, even when you’re not), you usually want your subject’s eyes in focus. Not their cheek, their nostrils, nose hairs, unibrow, et cetera. And it never fails that when you’re close in on your subject, your autofocus will focus on anything but the eyes.
  • Moving subjects: This one may seem counterintuitive, and it takes practice, but if you’re dealing with a moving subject, it can help to manually focus rather than hoping the AF locks on correctly. It’s especially true when you’re dealing with a subject that’s moving through a scene with lots of foreground/background distractions.
  • Static Subjects: If you’re photographing, say, your dinner, it’s not likely to run away on you (I hope). Using manual focus at a time you don’t necessarily have to can be useful because it forces you to slow down, but also because it can give you the ability to fine-tune what you want in focus.
  • Prefocusing: This isn’t purely manual focusing, but I’m going to add it here because it’s related. If your AF system is having difficulty acquiring your subject for one of the reasons above (or any of the others) but you don’t want to turn AF off for some reason, you can manually focus on your subject (or at least get close to correct focus) and then let the camera take over.

Last, but by no means least, there’s the Stubborn Camera. There will be times that your camera will, for reasons known only to itself, focus on anything and everything but your subject. You could be taking a photo of a black spider on a white wall, and your camera will seemingly fall madly in love with a nondescript part of the wall, totally ignoring the spider. Or it will focus on the clouds, rather than the bear that’s looming over you, threatening to… well, in that case, I think focusing is the least of your problems.

Have any tips you’d like to share? Comment below, or feel free to inbox me!

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