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What’s the Best Method to Autofocus? Center Point or Outer?

Mike Pouliot
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03/29/2011
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One of our readers sent us a question a few days ago and we thought it would be good to respond in a post so the other readers could learn and share their thoughts and experiences. The reader’s mail brought up a good point: is it best to use the outer focusing points or the center for the sharpest image and the most accurate focusing?

Below is from the reader’s email…

“I normally use the middle focal point because that way I know what I want will be in focus and then recompose as was suggested by another photographer as well as yourself. The question is, when I move to recompose (I’m not talking drastically, but if I center my subject and then shift so they are now on the right of my field of view so I can catch something behind them as well for example), doesn’t that lose my focus on my subject since they are no longer where the camera focused?”

Side note, the reader uses a Canon 60D which is good for me as I have a Canon 5D so we will both speak the same lingo. That being said, what I have written below will apply to any brand camera; just keep in mind that some of the brand specific terms may be different.

This is a good question which is often discussed in many blogs and forums. Some photographers swear by the focus and recompose method while others will only focus by manually selecting a focus point. There are solid arguments for using either technique and we could debate them for the rest of eternity.

That’s why I just say use what works for YOU.

Personally, I use both. If you decide that the focus and recompose method works for you, remember the following:

  1. Make sure you have your camera’s AF mode set to “one shot”. If you have your AF set to AI Servo or AI Focus, your camera may try to adjust focus again when you move the camera to recompose. This may be the problem our reader is referring to in his question. For non-Canon users, this means Single focus vs continuous focusing.
  2. Don’t forget metering. If you are using your camera with the default settings and you are not manually locking exposure with the * button, you may have metering issues i.e. pictures may come out under or over exposed. In the default setup (no custom functions), the camera locks focus and exposure when you half-press the shutter release button. If you meter on one area and then move the camera to another, you may need to meter again in this new area to obtain an accurate exposure. One trick that I use is my camera’s custom functions.
    On my Canon 5D, I use the * button on the back to focus and then I half press on the shutter button to lock exposure. This allows me to perform each task separately. I can focus on one area and then meter off of another. I can also focus and meter off of the same area if needed. If you don’t want to mess around with custom functions, try using the exposure lock button (* button) on the back of your camera. This will allow you to lock your exposure on a specific area and then refocus or recompose your shot without messing up your meter value.
  3. This one is a little more technical: Keep your focal length, aperture and subject proximity in mind when shooting. These three factors go into producing depth of field (DOF). There are a bunch of sites and apps available that have DOF calculators which tell you exactly how much of your photo will be in focus; this can be a handy tool to have on-hand. I could get very technical here (focus plane and lots of math), but let’s try keep things simple. When shooting at a wide aperture, as you move closer to your subject, more of the background area becomes out of focus. This means when aperture is held constant, the area in focus becomes narrower as you move closer. Say you are shooting a Canon 50mm F/1.2L at it’s minimal focusing distance of 1.5′. According to DOFmaster.com, the total area in focus is only 0.22″. This is an insanely small DOF. Any small shift in movement will cause you to misfocus. If you just breathe you will be out of focus…never mind trying to focus and recompose. As you move farther back and/or stop down your aperture value, the area in focus increases providing a little more room for error. Say you back off to 10 feet with the same lens and change your aperture value to F/2.5. The new area in focus becomes a much more manageable 21.96″. This range and aperture value provide you with more room for error but it does not give you the same look and feel to your shot. My suggestion is when you are shooting at a close distance with a wide aperture, it’s probably best to use the focus point closest to your subject.

The only time I would advise all photographers, regardless of preferred focusing method, to give the focus and recompose a try is shooting in low light conditions. Like other cameras, my Canon 5D has a wee bit of trouble focusing in less than ideal lighting. My only hope in low light is the center AF point. With most DSLRs, the center focus point is much more sensitive than the surrounding focus points. Using the focus and recompose technique allows me to use the center AF point to quickly lock on focus and recompose as needed.

I hope this helped our reader and any others that may have had questions about this focusing technique. As always, feel free to leave your thoughts and comments on this topic below.

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