Nothing messes up a shot like having everything turn out blurry, and this is a common problem with any sort of camera, but sometimes an acute problem with digital. There are a number of things that can cause a picture to be blurry, including:

The camera or subject may have moved during exposure. This can be corrected to a degree by using a faster shutter speed, putting the camera on a tripod, panning with subject motion, and so forth.
The focus may be incorrect.
The lens may be too “soft”, even when in focus.

Problems with motion are best solved by careful planning. Any given subject will have a likely set of conditions under which photography is best. Some of the conditions aren’t much under your control as a photographer, so you try to control the ones you can.

In general, you’ll want lenses that have large maximum f-stops, since that will let you push up the shutter speed if necessary and still expose correctly. Depending on the combination of shutter speed and the subject distance, and on available light you’re likely to encounter, that will determine the film speed (or ASA setting on a digital camera). For this sort of lens stuff, see our tip on lenses.

The problem with focus is more knotty, because it can arise from a bunch of factors. One of them that’s also dealt with in the lens tip is the question of depth of field. There are a couple of others that we want to cover here, and one in depth.

The easy focus issue is the manual versus autofocus issue. Most modern cameras have autofocus, but it’s not always going to work. At very low light levels, for lenses with a small maximum f-stop, or with many teleconverters and nearly all extension tubes or bellows attachments used in close-ups, you won’t be able to autofocus at all. If that’s the case, it opens a can of worms, make no mistake!

Manual Focus and Hyperfocal Distance

First, if you’re going to manually focus it’s absolutely critical that you adjust the diopter setting of your camera’s viewfinder accurately. Put on a nice lens, pick a bright subject with lots of edges, and let the autofocus do its job. When the image is focused, adjust the diopter setting till it looks good through the viewfinder. Make a note of where this setting is, because it can get jarred out of kilter if you aren’t careful in packing or handling the camera.

Once you have your diopter set, you’ll have to set the camera/lens up for correct manual focus operation. On my S2 and N80 (same body but the S2 is a Fuji digital), the focus control is on the left side of the camera body, left and at the low end of the lens as you look through the viewfinder. That has to be flicked into manual mode. In addition, some lenses have a manual/auto switch or slide that has to be tweaked. Sigma’s 24-70mm EX f2.8 is like that. Not only do you have to get all these switches into the right place to use manual focusing, you’ve also got to get them back into autofocus mode when you’re done.

When you manual focus, first get the image sharp to the eye and then use the focus indicator in the viewfinder (in the S2 it’s a dot at the extreme left of the status bar) to be sure you’ve gotten it exactly right.

Manual focus is a really nice process if you get an understanding of what is called the hyperfocal distance. For any lens and any f-stop, there’s a focus distance that will render everything sharp from half that distance to infinity. Set the focus to this value manually and you have a sharp image anywhere in that range.

The question is how big “that range” is. Not very, unfortunately. If you take my S2 with a 100mm lens set at f8, the hyperfocal distance is about 200 feet. Focus at that distance and everything from 100 feet to infinity is in focus. Well, that’s helpful for your average shoot, huh? First, try reading your lens focus ring to find the 200 foot setting. Second, 100 feet is a tad far for most subjects. Moral: To make hyperfocal distance useful you probably have to get out of the telephoto range. Remember, that 100mm lens is a 150mm telephoto on the S2. If you move to a 50mm lens at f11, though, the hyperfocal distance is about 36 feet, meaning that from about 18 feet to infinity you’re in focus. That’s pretty good.

Autofocus

If you hated that process, you might be tempted to just keep things in autofocus mode. In truth, many won’t have a lot of trouble being forced to use manual focus because they won’t use teleconverters or other lens accessories and won’t shoot under dark conditions. But unfortunately, autofocus can really mess you up, too. That’s why most of this particular tip is about autofocus and its issues. Let me start by reminding my readers that I’m a user of Nikon cameras and the Fuji S2, which is built on an N80 body, so this tip is explicitly for that style of autofocus.

If you look through an N80 or S2 viewfinder (or that of other higher-end Nikon models as well), you’ll see a small center rectangle and four others arrayed about it, above, below, left, and right. These rectangles mark focus areas. In the old days of auto-focus, there was a single focus area in the center. These days, cameras let you select from several such focus areas to simplify off-center composition and to handle moving subjects.

Not all focus areas are created equal, though. The N80, S2, and D100 (that all share the same body/system) have a center focus zone that works with either horizontal or vertical edges, which means that as long as there’s some edge contrast in the center of the scene, you can achieve autofocus using that central sensor. The top and bottom sensors are oriented horizontally, and the left and right are vertical. An edge has to cut the sensor to be “sensed” so the top and bottom sensors are good for vertical subjects and the left and right for horizontal. Confused? It gets better. In the meantime, just leave the thing set for the center zone and read on.

Nikon N80 autofocus is based on several different parameter settings, and these are similar on most Nikon DSLRs, including the D2X and Fuji S2/S3:

“Continuous” or “Single” servo focusing mode. This is set on the top left-hand dial of the camera, and it determines if the focus mechanism is supposed to lock on a subject that’s stationary, and thus stay fixed once focus is achieved (single-servo) or if it is to continuously adjust focus because the subject is moving toward or away from the camera and thus changing the focus point (continuous servo).
“Focus area”, which determines whether the camera focuses based on a single selected focus area (single-area AF) or on the dynamic evaluation of multiple areas (dynamic AF).
The specific focus area selected, among the five areas visible in the viewfinder.
The setting of the “closest subject priority” setting of the custom settings menu of the camera.

Before we can get to the combinations of all this, we have to address the knotty hub of the issue, which is just what dynamic AF means.

Dynamic autofocus let’s the camera select the focus area to use if the subject moves. That means that whether you select an initial area or not (which we’ll get to); the movement of the subject to another area will move the focus determination with it. Single-area AF means that you pick the focus area, and if the subject moves out if it—too bad. In this mode, you can decide whether you want closest-subject focus priority or not. All that means is that you can decide if you want the camera to select the initial AF area to be active (based on which contains the closest subject to the camera) or whether you make that determination manually. Now let’s apply this to the different combinations of the other parameter settings.

First, let’s assume single-servo focus mode. In this mode, focus lock must be achieved to fire the shutter. Under these conditions, you have the following possibilities:

Single-area AF. With this mode, you select the AF area to be used. Whatever is in that area determines the initial focus. If the area contains a moving object, focus lock will not occur. If the object moves once focus lock is achieved, lock is lost. This setting is usually described as best for stationary objects.
Dynamic AF, closest subject priority is set. In this mode, the camera picks the initial focus area based on which contains the closest object. Lock is set on that area, but if the object moves to another area during focusing, the other area is used. Once lock is established, the movement of the subject breaks lock. This mode is said to be good for objects that may be moving about in the field of view during focusing, but where the closest object to the camera within any of the focus areas is unambiguously the thing you want to focus on.
Dynamic AF, closest subject priority off. In this mode, you must select the AF area that will be used to first attempt focus. If the subject moves from that area during focus, it will be tracked to other areas. If movement occurs once focus lock is achieved, lock is broken. This is said to be pretty much the previous mode without the closest-subject capture.

Now let’s try the same in continuous servo mode. In this mode, the camera will attempt to track a subject with focus, but the shutter will fire even if lock is not achieved, which means that you have to be careful to watch the focus indicator. Here are the options:

Single-area AF now will continue to try to lock on a moving subject. However, that lock might not occur and the camera shutter will trip anyway. Thus, if the object moves out of the zone of the selected AF area, you’ll not achieve proper focus.
Dynamic AF with closest subject priority will now act as the closest thing to focus snap-shot you can get. The camera will track the closest subject however it moves through the AF areas. Again, the shutter will fire when you press all the way on the release regardless of the current focus state.
Dynamic AF without closest subject priority now tracks the object/subject from the zone you selected as the start to wherever it moves. Same shutter comment applies.

OK, that sounded a little complicated, but why all the fuss? OK, here’s the kicker. When is the subject moving and when is the camera moving? Simple question, bad problem. If you are shooting with a telephoto lens and hand-holding, or if you’re on an unstable platform, you may get camera movement. Even if your shutter speed is high enough to stop the action, you may get blur because the movement has tricked the AF into thinking the subject is moving and it’s reacting according to one of the conditions above.

Last topic on focus is the issue of using AF lock. The default way of taking a picture is to press on the shutter till you hear a click, which is a pretty straightforward approach. Most people who use the Nikon-style cameras also know that if you press down halfway on the shutter, you will lock in the focus. You can hold that half-pushed state and change composition. This is often a better way to handle a subject that you want to have off-center than using the focus area selection process (which, when you change, you’ll forget to change back). There’s also an AE/AF lock button on the back of the camera, and it’s possible to change the custom settings of the N80 and S2 to use that back button as an on-off AE lock, meaning that pressing it will lock the current exposure setting until you fire the shutter or press again. That lets you set exposure and focus on different areas of the picture without disabling autofocus. If you want to experiment with this, read the manual carefully and then do some personal fiddling before you try it in the field. It’s not totally intuitive.

New cameras like the D2X and D2H have a "Group Dynamic" mode that's essentially like dynamic AF but limiting the dynamic lock to a specific group of AF sensors. You can apply the same general rules for this mode as for the dynamic mode, by the way.

Recommendations

I hate to make recommendations, because no matter what you say you’ll find people who disagree. If you’re one of them, the simple solution is not to read this (or go ahead and read it, but don’t bother telling me you don’t agree)!

First, I think that closest-subject priority is useful only if the “subject” is photographed against something that’s a lot further away—like the sky. For birds in flight and other stuff silhouetted against distant background, it’s a great approach. Use it in single-servo mode if the subject isn’t changing distances on you; otherwise use continuous-servo mode.

Second, dynamic AF is useful only if you’re using continuous servo mode or closest subject priority. I’d avoid it in particular for any subjects photographed in the midst of other stuff; a single animal in a group, a person in a crowd, a building in a skyline. The problem is that the dynamic area selection may end up selecting an area that doesn’t contain the thing you want to photograph. With long telephoto lenses, dynamic AF mode is a particular killer. Maybe I’m old-fashioned, but I’m uncomfortable with the camera competing with me to compose the shot! Handle a few things on your own, and focus is probably a good one to start with.

Third, you’ll need continuous servo and dynamic AF if you’re photographing things that are moving around a lot, both side to side and in and out with respect to the camera. Otherwise you’ll never get focus lock. Just be careful that you really have lock when you shoot! I can’t tell you how many N80 shots I blew because of this, and then I blew some more with the S2 because of a quirk: the Fuji S2 comes with dynamic AF and closest subject priority set by default! Moral: Check those darn CSM settings and be sure that the factory defaults are what you want.

For my own part, what I find convenient is to enable dynamic AF as a default and also enable closest-subject priority for single-servo mode, but not for continuous server mode. When shooting under conditions where closest-subject priority isn’t logical, it’s easy enough to disable dynamic AF, which of course disables closest-subject. This way I have closest-subject available for pictures that really demand it, like snap shots of birds. I can also simply flick to continuous servo to keep dynamic AF but lose closest-subject priority.

Whatever you decide to do, stick to it. The worst thing you can do with any setting like this is fiddle continuously with it, because you’ll forget how it’s set. It takes some effort to change the closest-subject priority setting in particular, so get a rhythm and stay with it in all your shooting.