By Joseph Kashi, for the Redoubt Reporter
Camera makers often imply that you’ll only get good photographs if you’re using their most expensive equipment. That’s nonsense. Cameras don’t kill pictures, people kill pictures.
Excellent optics and cameras can help you capture high-quality photographs under a wider range of lighting conditions, but buying expensive camera equipment does not ensure good photographs any more than buying a match-grade target rifle turns a rank amateur into an expert marksman.
I’ve seen excellent and provocative photo essays made by pros using only a simple cell phone camera, whose capabilities are less than the cheapest, entry-level, point-and-shoot compact camera. An experienced photographer knows how to avoid common mistakes that kill pictures and how to use any camera’s limitations to his or her advantage.
Most common photo mistakes are easily avoided. This week, we’ll explore how you can control where and how your camera focuses, a fundamentally important skill. Although we don’t always want a photograph that’s tack sharp from corner to corner, it’s important to know how to achieve sharp focus when we need it.
Undesirably fuzzy pictures often occur because a camera may be badly out of focus or because important parts of the subject may be blurred if there is not enough “depth of field” (focus).
On the other hand, too much may be in focus, resulting in what becomes a distracting background. That detracts attention from your main subject. How you choose to work with focus, sharpness and background depends upon your subject and how you wish to show it. In a landscape, for example, we typically desire that almost everything be quite sharp. On the other hand, a wedding photograph of the newly married couple embracing is more effective when the background is so blurred that all of your attention is directed upon the couple.
Undesired focus problems can occur for many reasons, most of which can be easily corrected by adjusting your technique when you take the picture. Sometimes, though, a dSLR’s autofocus mechanism may focus in front or in back of your subject, an optical inaccuracy that requires knowledgeable adjustment of your camera. Correcting that problem may or may not be feasible.
This week, let’s look at how you can focus more accurately upon your subject.
Almost all cameras are now equipped with some sort of autofocus mechanism. dSLR cameras typically focus faster than compact cameras because they use a form of separate optical comparison that works through the mirror and optical viewfinder, independent of the image actually focused upon the sensor. With a dSLR camera, focus speed is limited by how quickly the lens can move mechanically rather than upon any optical limitations.
The drawback is that some dSLR cameras and lenses may actually focus in front or behind where this independent optical assembly thinks that they should be focusing. Such “front” or “back” focus can result in at least some blurring of the main subject.
The most common tool for measuring whether a dSLR camera focuses accurately, and then making the right corrections, is “LensAlign,” available from www.amazon.com or www.lensalign.com. Many semipro cameras, such as the Pentax K20d or K-7, allow an experienced user to adjust the camera body through a menu setting so that each lens focuses correctly.
Compact cameras use a form of contrast detection focusing. Basically, the camera searches for sharp, high-contrast edges and then moves the lens back and forth until that edge’s contrast reaches a maximum. That takes more time.
In a high-quality compact camera, contrast focusing can be quite accurate in good light because it’s working directly with the image that the lens focuses upon the sensor. Contrast focusing has two drawbacks: it’s usually slower and ideally it should find a sharp, high contrast edge near one of the sensor’s focus detectors.
Without a high contrast area, a camera may not be able to focus at all under some circumstances. One example would be a landscape photograph in which most of the picture is sky or fog. There’s nothing sharp and contrasty in the middle of the frame that the autofocus sensors can use, and so correct focus is a hit-or-miss process.
Most cameras have a variety of focus settings and several focus sensors, which are usually arrayed in the center two-thirds of the image sensor. Unless manually overridden by you, whichever focus sensor the camera chooses as its focus point determines where the camera will focus.
An autofocus camera chooses its focus point based upon preprogrammed camera instructions. Many assumptions are built into these preprogrammed instructions, such as an assumption that you want to focus on something that’s closer rather than farther and that your subject is near the middle of the picture frame. These are frequently valid assumptions, at least for the casual snap-shooter. There are, however, times when a more experienced photographer needs to override them.
A selected autofocus point may or may not be correct for your subject and picture intent. However, in all but a few cameras, a small red dot in the viewfinder or picture area will show you precisely what the camera’s focusing upon, allowing you to decide whether to accept that focus point.
There are several ways to make focus corrections that work with almost all cameras.
Higher-end cameras allow you to choose the precise focus sensor. If that’s not feasible, then you can set the camera to center “spot” focus, and aim the camera directly at the point you wish to focus upon. Then, half-press and hold the shutter release. This focuses the camera on the correct point and holds the focus while you re-center the photograph and compose it. Fully depressing the shutter completes taking the photograph. Incidentally, this is a good technique for capturing quick action with a less expensive camera whose contrast detection focusing is inherently slower.
Low light is an especially difficult condition in which to achieve good focus with a compact camera. For that reason, higher-end compact cameras often include an orange or green focus light that illuminates a dark subject. Although this may be intrusive, it definitely helps in low light.
Most modern digital cameras also have manual focus options. Unfortunately, these are often less usable than traditional film cameras, which included manual focus aids visible in the optical viewfinder. Manual autofocus in digital cameras relies upon a highly magnified center image. I find this more difficult to use but it may work well for you. Despite that, it’s still the best option in a difficult focus situation, especially if you use a tripod or some other steady camera support.
Once you’ve accurately focused upon the correct point, then you can hold that focus using the “autofocus lock” button that’s built into many higher-end cameras.
Many cameras include a button that allows you to manually set the general zone where the camera focuses. This may be more than adequate, especially with distant subjects.
Some distance in front of the point of precise focus and a greater distance behind it are also in acceptably sharp focus. This is termed “depth of field,” although it’s really depth of focus. Using “depth of field” is both important and fairly easy. We’ll cover it next time.
Local attorney Joe Kashi received his bachelor’s and master’s degrees from MIT and his law degree from Georgetown University. He has published many articles about computer technology, law practice and digital photography in national media since 1990. Many of his technology and photography articles can be accessed through his Web site, www.kashilaw.com.
