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Tuesday, November 18, 2008

10 Tips For Better Autofocus


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10 tips
3 Acadia National Park, Maine

3 Change Your AF Point
Most cameras allow you to select a specific AF point. The standard way that autofocus works in cameras is for the camera to choose what it thinks is the best focus point from an array of AF points across the scene. This works in a lot of situations. But if you have a subject that must be sharp in a specific part of the composition, you’re best off changing this default setting to a specific AF point where you need sharpness. One example is an animal that continually comes to a specific area in the composition. You need to be sure the animal is absolutely sharp, yet the subject may be at slightly different distances from the camera so that manual focus can’t be used. Simply select an AF point where the animal is likely to be.

4 Know Your Camera’s Idiosyncrasies
It’s great fun for photographers to get together and debate the relative merits of different cameras. And there’s no question that there are differences in the way that cameras handle autofocus. While the debate may be fun, it doesn’t help you get better pictures with your camera. You need to learn the idio-syncrasies of autofocus with your camera. What does it do best? Where does it seem to have problems? This comes from using your camera in all sorts of situations. One of the great things about digital photography is that you can shoot lots of pictures in order to see what your camera can do, yet there’s no cost to shooting those pictures.

10 tips
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Sure, we’d all like the latest and greatest of the newest cameras, but until we can afford that new purchase, we need to understand how to get the best from the equipment that we do have. Every time that I purchase or test a new camera, I always take it out and play with it before I have to use it seriously. I want to know the camera’s idiosyncrasies regarding autofocus and other controls. It’s important to work with the camera in your hand and get the most out of it rather than worry that it can’t do something it wasn’t designed for.

5 SAF Vs. CAF Vs. Hybrid
Your camera offers at least two options for autofocus: single shot (SAF) and continuous (CAF). Single-shot AF locks down the focus and won’t allow the camera to shoot until focus is confirmed. This is an important type of focus for most standard nature scenes where focus doesn’t change (and shouldn’t change). Continuous autofocus allows the camera to focus continually as you take pictures, updating the progress of a moving subject, for example.

10 tips
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A third option on many cameras is a hybrid. This type of autofocus allows the camera to decide when to use single-shot autofocus and continuous autofocus. This has never been a choice that I’ve liked. It seems like the camera is always choosing the wrong type of autofocus and screwing up my focus as I shoot. I’d rather choose a specific type of autofocus based on the subject and movement of the subject.

6 Watch For Bright Light
Bright light in your composition, especially the sun, can confuse your AF system. A dramatic way of photographing a landscape with trees is to shoot it against the sun so the sun creates a starburst pattern through the trees. But that dramatic effect also can cause problems with autofocus. Try moving the camera to autofocus without the sun and then reframing the composition. You also might have to change the camera to manual focus for scenes like this.

10 tips

6 Shenandoah National Park, Virginia
7 Beware Of AF Up Close
Autofocus often has trouble when you’re dealing with close subjects. Depth of field is so shallow that even a slight change in focus can make the difference between a good picture and one for the trash. Very often the camera will choose the wrong point for focus up close. For this reason, many of the best macro shooters use manual focus for close-up work. There’s also a trick to using autofocus up close. Move your camera around and lock focus on an important part of your subject. Keep that focus locked and gently move your camera toward and away from the subject until you have exactly the right spot in focus. Take the picture. Another thing that drives you crazy up close is when the camera starts focusing to infinity. Many lenses have focus limiters for just this reason. If yours has such a switch, set it so that it only focuses at a close distance when you’re doing close-up photography.

8 Faster Lenses Help AF

A fast lens is a lens with a wide maximum aperture, such as ƒ/2.8. If you need fast autofocusing, you need a fast lens. Most zooms are slower lenses with maximum apertures of ƒ/4 or so, especially the compact zooms. If you have an extended range zoom that’s also compact, you can find that the lens speed gets very slow. For subjects such as landscapes or flowers, that’s not a big deal. For fast-moving wildlife, a slow lens can have a big effect on how quickly you can get the animal in focus.

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