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Tuesday, April 26, 2011

Boost Your AF Performance


How to set up your camera and lens to get quick response when you’re shooting fast-moving subjects like wildlife



This Article Features Photo Zoom

Birds flying directly toward the camera are easier to deal with than birds flying erratically across the frame. Keep the AF point on the bird’s head (very difficult, but gets easier with lots of practice). Don’t worry about the composition; you can crop as desired when you process the image. Concentrate on the moment and keeping the AF point on the bird’s head.
Nikon D300, AF-S NIKKOR 300mm ƒ/4D IF-ED, 1/4000 sec. at ƒ/4, ISO 800

Today’s DSLRs are amazingly quick in their AF performance and firing rates, but you can make them even quicker by setting them appropriately. My favorite subjects are birds, and they present a serious action challenge with their quick and erratic movements. I appreciate all the help I can get from my camera. I discovered birds after more than 25 years in photography, and I did my early avian photography with a manual-focus Nikon F3 35mm SLR coupled with an 80-200mm zoom. As the AF film SLR and then the DSLR arrived on the scene and matured, I looked for ways to squeeze every bit of performance out of my cameras and lenses for action shooting. Here are some things I’ve learned from the more than 70 DSLRs I’ve been able to test and use in the field (a fringe benefit of working for photo magazines is getting to try lots of gear). Birds are my favorite subjects, but the techniques I’ve learned should help with all wildlife and even sports-action photography.

Use Release-Priority AF
1 Set your DSLR for release-priority AF rather than focus-priority AF (assuming it permits you to do so). Focus-priority AF locks the shutter release until the camera thinks the image is in focus. It was developed for point-and-shoot cameras to keep snapshooters from accidentally taking out-of-focus images—it’s fine for that, but it’s not for serious photography. When I push the shutter button to take a shot with a DSLR, it’s because I want to record what I see in the viewfinder at that instant, and the only correct response for the camera is to record it. I don’t want the camera telling me “You can’t have this moment because my circuits haven’t decided yet whether it’s in focus.”

Of course, in release-priority AF, the shutter will fire whenever you fully depress the shutter button—whether or not the image is in focus. So make sure the image in the viewfinder looks sharp before you fully depress the shutter button. If your DSLR doesn’t provide release-priority AF, you can still get good action shots, but focus-priority will cost you lots of shots, where the camera just won’t fire.

Use The Center AF Point
2 Use the center AF point only. This is the most sensitive and accurate point, and demands less of the camera’s processor than using all the AF points. If you activate additional AF points, it will slow things down a bit. Today’s AF systems are amazingly quick, but when speed is of the essence, use only the center AF point.

But be sure to keep that point on the subject or the desired portion of the subject like an animal’s eyes. That takes lots of practice, but do it. Put in the time, and you’ll see the results! Don’t worry about composition; most flight shots have plenty of space around the bird, so you can crop as you wish when you edit the image. Get the moment, with the AF point on the bird’s head. If the AF point falls on the wingtip of a large bird, the head will be out of focus.


Cameras that have an external AF-S/AF-C/MF switch (like higher-end Nikon DSLRs and this Pentax K-5) make changing modes with the camera at your eye easy. Many mid- and high-end DSLRs have a programmable thumb-operated AF-on (or AF-lock) button on the back. You can set this so it activates AF and locks focus when released, or so it locks focus when pressed, either way allowing you to stay in continuous AF mode for both action and static wildlife shots.

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