I know it's happened to you, because it's happened to me, too. It happens to everyone. You point your camera at something really cool. You shoot. You check your LCD. Awesome! You just grabbed the most amazing shot ever. You go home and open up the photo on your computer. And it isn't sharp.
Oh no! What happened? What went wrong? And most importantly, how can you stop it from happening again?
Well the short answer is, you can't always stop it from happening. Unfocused images are just par for the course when you're a photographer. But the good news is, you can greatly reduce the number of unfocused images on any one memory card just by following a few simple tips.
#1: Even Smart Cameras can Sometimes make Stupid Decisions
Cameras don't know anything about the rule of thirds. In fact, most inexpensive cameras default to breaking the rule of thirds by focusing on whatever is dead-center in the frame. So while you're faithfully following that rule of thirds and placing your subject on the right or left side of the frame, your camera is going, "Hmm, I guess that's not the focal point anymore, I'll just focus on this dumb rock in the distance instead of on that lovely white egret that Photo Joe just put in the left third of the frame."
A smart DSLR, on the other hand, can actually evaluate a scene and make a judgment call about what the subject might be, and then select a focal point based on where that subject is in the frame. This is about as automatic as it gets, and as with all fully-automatic features, it's a less than perfect solution. It will probably make the right choice most of the time. But when it makes the wrong choice, it's almost certainly going to be on that once-in-a-lifetime awesome shot that you can't go back and do again.
#2: Focus and Recompose
Fortunately, if you own a modern DSLR, you don't need to rely on your camera to make focusing decisions for you. Modern DSLRs have some pretty sophisticated tools available for achieving focus - you just need to understand how and when to use them.
To take more control over your autofocus, start by using focus-lock. To use focus-lock, center your subject in your viewfinder and press your shutter button down halfway to focus. Then recompose and shoot. Now, this works great at smaller apertures because your depth of field is great enough that moving your camera a little to the right or left isn't going to affect your focus. If you're shooting at very large apertures, though, even a slight change in angle may mean the difference between a sharp subject and a blurry one. For this reason, the focus/recompose method may not always be the best one.
#3: Know your Focus Points
Modern DSLRs have an autofocus "area" mode, which lets you choose the way your camera focuses on a subject. This is usually controlled by a switch at the back of the camera, and will include a single-point focus mode, a dynamic area mode or an auto area mode. In single point mode, you manually choose where you want the camera to focus. Some photographers avoid using this mode because it can be a bit clunky at first, but once you get used to it, it gives you a lot of power and control over your images.
In single-point mode, you use the joystick on the back of your camera to move the focal point in your viewfinder until it lands on the part of the frame you want to be in focus - your subject's eye, for example. Then as long as you keep your subject under that focal point, that's where your image is going to be sharpest.
Dynamic area mode, on the other hand, gives you a little more help when shooting with continuous servo. You'll still be selecting the points manually - but if your subject leaves the point you selected, your camera will track it so that it will stay in focus without you having to keep it under that selected focus point. Selecting dynamic area mode only makes a difference in continuous-servo mode; in single servo mode focus will remain on the point you selected regardless of where your subject goes.
Auto-area mode is exactly what you probably guessed: your camera decides which part of your scene is the subject, and makes all the focusing decisions for you.
#4: Use AF-ON (back button focus)
This feature exists on almost all modern DSLRs, and I'll bet most owners of those DSLRs don't know what to do with it. Essentially, this button removes the job of focusing from your shutter button. Instead, you use the AF-ON button to focus, and the shutter button to actually shoot the picture. This is particularly handy because it stops your camera from refocusing every time you press your shutter button, which can result in images that don't have the focus where you intended it to be. When you use AF-ON (otherwise known as back button focusing), you choose a focal point, use the AF-ON button to focus on it, and that's that. The focus stays on that point until you decide to change it. (Note: giving focus control entirely to AF-ON may require a menu change in your camera's settings.)
Why is this useful? Because anyone who relies on that halfway-down shutter button knows that unless you keep your finger there indefinitely, your camera is going to refocus when you try to take the picture. This means that you have to switch to manual focus whenever you're prefocusing on something, or else just keep your finger there and hope it doesn't slip and take a premature shot, or that you don't let go a little and mess up everything you'd just prefocused on.
#5: Use Focus Tracking (continuous servo focusing)
Most DSLRs give you three different focusing modes, controlled by a little switch in the front of your camera. The first is single-servo focusing. In this mode, you focus the camera and take the shot, and the focus stays the same regardless of what happens in the scene. The second focusing mode is manual, which shuts off the autofocus system entirely and leaves the whole endeavor up to you. The third option is continuous servo focusing, also called "focus tracking." This is useful for shooting fast-moving subjects.
Moving subjects pose a special focusing challenge, especially those that are moving towards or away from the camera. Without focus tracking, you need to refocus each time you want to take a shot or else rely entirely upon guesswork, such as prefocusing on a predetermined spot and then hoping your subject actually lands there. If you set your camera to continuous servo focusing, however, your camera's autofocus will make slight adjustments as your subject moves, allowing you to fire off as many shots as you like without having to muck around with the focus.
Bonus: Other Common Causes of Blurry Photos
There are also other causes of blurry images. Having an incorrect focus is just one of them. See the other three in my article and video: The Top 4 Causes of Blurry Photos, And How To Fix Them
We've come a long way since the days when we had to use a focusing ring to get a sharp subject, but without a good understanding of all the tools your DSLR gives you for controlling focus, you may end up with as many blurry shots as those golden-age photographers, who had to sacrifice expensive film frames on the altar of manual focus. Today we have it easy - our cameras know what we want, provided we actually tell them. Don't let your camera make all the decisions for you, but that doesn't mean you shouldn't also take full advantage of all that focusing tech that we modern photographers are blessed with.
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