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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

Pro DSLRs have more AF points, but you’ll still get quickest AF performance with only the center point active. The center point is also generally more sensitive than the others.
Program The AF Button
8 Many action photographers like to separate AF activation from the shutter button, switching the function to the rear AF-on button. Most AF SLRs will let you do this via a custom function. That way, you can activate focus by pressing the AF button and stay in continuous AF mode at all times, releasing the rear AF-on button to lock focus on perched birds. Note that with some cameras, the AF-on button won’t activate the image stabilizer in the lens although, as pointed out in Tip #6: Switch Off The Stabilizer, I don’t recommend using the stabilizer for flight shots.

Switch Off The AF Illuminator
9 The AF Illuminator is effective only out to around 10 to 12 feet. You’re not likely to be doing action shots at that range, and the illuminator slows things down, so switch it off. Besides, if the light level is so dim that the illuminator fires, you’ll be doing slow-shutter blur effects anyway, not sharp action shots.

Use Manual Exposure Control
10 Today’s AE systems are almost instantaneous, but for quickest response, preset the exposure manually. As a bonus, if you preset the exposure manually for the subject, you won’t have to worry about the meter being fooled as it travels across bright and dark backgrounds. Having to determine and set and reset exposure compensation while tracking a quick-moving subject doesn’t help produce sharp action images.

Use The Right Shutter Speed
11 Normally, you’ll want to use a fast enough shutter speed to sharply “freeze” the subject in the image; generally, this will require 1⁄1000 sec. or faster. However, this can vary depending on the subject’s speed and direction of movement and the shooting distance. You may want to experiment with different shutter speeds, including slow-shutter blur effects, both handheld and with support (see Tip #15: Try A Camera Support).

Try A Higher ISO Setting
12 Most lenses are at their best a stop or two from wide open, e.g., ƒ/5.6 or ƒ/8 for an ƒ/4 lens. This also provides a bit more depth of field to get more of a large subject sharp. But you also need a fast enough shutter speed to stop the action and to handhold a long lens. Most current DSLRs can produce excellent image quality at ISO 400-800, which provides some leeway for lower-light situations, although ISO 100-200 generally produces the best image quality with most DSLRs.

Experiment with different shutter speeds, ISO settings and apertures from wide open to two stops down from there, and see what works best for you.

Set The Advance Rate To Suit The Subject
13 High-speed advance gives you a better chance of catching that perfect moment, but low-speed advance gives the AF system more time to nail focus between shots. You’ll have to see which works best for you with your camera. I sometimes use high-speed advance, which is 6 to 10 fps with my cameras, and sometimes low-speed, which is 3 to 5 fps with my cameras. Either way, fire short bursts so you get a variety of “decisive action moments.”


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