Beginner photographers typically say that they want their photos to be "sharp and clear." That's especially true for applications like online auctions, for which the image shown in Figure 3.15 was prepared. When you're selling something on eBay, you want the entire widget to be reasonably sharp.
However, experienced photographers know that a bit of blurriness used intelligently can turn an ordinary photograph into one that's special—a subject that appears to merge with its background. Selective focus, choosing exactly what parts of the image are in sharp focus and which are not, is a powerful creative tool. Blur can also make other portions of an image appear to be sharper, by comparison. Figure 3.16 shows some flowers (at left) photographed with abundant depth-of-field, so the blooms merge with the background. At right, the reduced depth-of-field makes the flowers stand out from their background.
Unfortunately, the tool of selective focus is not as readily accessible to digital photographers as to those using film cameras, because the short focal lengths used for non-SLR digital camera lenses render virtually everything in most photos razor sharp. Shorter focal lengths inherently have much more depth-of-field than longer focal lengths, so that a 35mm (actual focal length) "telephoto" setting of your digital camera might provide the same field of view as a 135mm telephoto on a film camera, but the depth-of-field produced is closer to what the film photographer gets with a wide-angle lens.
Depth-of-field is also reduced at wider lens openings, and here, too, the digital camera's characteristics work against those who want to use selective focus. Most digital cameras don't boast a really large lens aperture, such as f1.4 or f2.0. The largest opening might well be f2.8, so you can't always count on shooting wide open to minimize depth-of-field. If you have your heart set on using selective focus and are not using a digital SLR, you can try two approaches (or combine them).
Figure 3.15. You probably want everything in your online auction photos to be in sharp focus.
However, experienced photographers know that a bit of blurriness used intelligently can turn an ordinary photograph into one that's special—a subject that appears to merge with its background. Selective focus, choosing exactly what parts of the image are in sharp focus and which are not, is a powerful creative tool. Blur can also make other portions of an image appear to be sharper, by comparison. Figure 3.16 shows some flowers (at left) photographed with abundant depth-of-field, so the blooms merge with the background. At right, the reduced depth-of-field makes the flowers stand out from their background.
Figure 3.16. In some cases, you'll want everything in your photo to be in sharp focus (left), while in other cases, you'll want to bring the main subject into sharp focus and allow the background to blur.
Unfortunately, the tool of selective focus is not as readily accessible to digital photographers as to those using film cameras, because the short focal lengths used for non-SLR digital camera lenses render virtually everything in most photos razor sharp. Shorter focal lengths inherently have much more depth-of-field than longer focal lengths, so that a 35mm (actual focal length) "telephoto" setting of your digital camera might provide the same field of view as a 135mm telephoto on a film camera, but the depth-of-field produced is closer to what the film photographer gets with a wide-angle lens.
Depth-of-field is also reduced at wider lens openings, and here, too, the digital camera's characteristics work against those who want to use selective focus. Most digital cameras don't boast a really large lens aperture, such as f1.4 or f2.0. The largest opening might well be f2.8, so you can't always count on shooting wide open to minimize depth-of-field. If you have your heart set on using selective focus and are not using a digital SLR, you can try two approaches (or combine them).
- Use the longest telephoto setting your camera offers. A camera with a long zoom range might offer the equivalent of 28mm to 200mm (with a film camera) that corresponds to true focal lengths of 7.2 to 50.8mm. That 50.8mm setting does have depth-of-field that is limited enough to allow selective focus, especially at wider apertures.
- Get in close. Depth-of-field is limited at close distances, too. If your subject matter lends itself to using your camera's macro capabilities, you might be able to reduce depth-of-field, as shown on the right in Figure 3.16.
Using Autofocus
As I mentioned in Chapter 2, digital cameras use various ways of determining correct focus automatically. Most work quite well; some, such as laser-based systems, work better under certain circumstances (low light, for example) than others. All have to be used intelligently.
Digital cameras often use a zone focusing scheme, similar to the zone metering offered by automatic exposure systems, in which the frame is divided into segments. You might be able to choose autofocus based on the center portion of the frame, or corners, as shown in Figure 3.17, which roughly represents the focusing zones of a Nikon camera I use. Cameras like my Nikon let you choose whether focus is based on the center autofocus area, or any of the other focus zones. In manual mode, that same camera allows you to select just one of the five autofocus target areas, which can be useful when your subject matter is concentrated in one of the corners of the frame.
Basic Focus Modes
In addition, most digital cameras have several automatic focusing modes to choose from. The most common modes include:
To make things even more interesting, some digital cameras have other parameters to choose from. The simplest of these are the focus ranges that can be set. These include:
As I mentioned in Chapter 2, digital cameras use various ways of determining correct focus automatically. Most work quite well; some, such as laser-based systems, work better under certain circumstances (low light, for example) than others. All have to be used intelligently.
Digital cameras often use a zone focusing scheme, similar to the zone metering offered by automatic exposure systems, in which the frame is divided into segments. You might be able to choose autofocus based on the center portion of the frame, or corners, as shown in Figure 3.17, which roughly represents the focusing zones of a Nikon camera I use. Cameras like my Nikon let you choose whether focus is based on the center autofocus area, or any of the other focus zones. In manual mode, that same camera allows you to select just one of the five autofocus target areas, which can be useful when your subject matter is concentrated in one of the corners of the frame.
Figure 3.17. Five or more "target" areas can be used to calculate the correct focus for an image.
Basic Focus Modes
In addition, most digital cameras have several automatic focusing modes to choose from. The most common modes include:
- Continuous autofocus. In this mode, the camera continually focuses the image (you'll know because you'll hear the autofocus motor constantly moving the elements of the lens) so you can frame and reframe the image and count on the picture always being (more or less) in focus when you're ready to take the picture. I say "more or less" because there is always a small amount of lag when you reframe the image on an object that is closer or farther away than the previous view. Some find this constant refocusing annoying. This mode can cause your camera's batteries to run down sooner, too, and can slow you down as you constantly wait for the camera to refocus each time you adjust the image. Continuous autofocus "locks" when you press the shutter release button down partway (or press a focus lock button, if available).
- Single autofocus. In this mode, the autofocus feature is activated only when the shutter release button is pressed partway. Once the image is sharp, focus is locked and you can continue to press the shutter release button to take the photo. This mode is easier on batteries and causes fewer delays when you're finally ready to take the photo. However, like continuous autofocus, this mode can contribute to a significant delay between the time you begin to press the shutter release and when the picture is taken. It's easy to miss that perfect expression or the peak action in a sports photo when using either type of autofocus.
- Manual focus. With manual focus activated, your digital camera lets you set the focus yourself. There are some advantages and disadvantages to this approach. While your batteries will last longer in manual focus mode, it will take you longer to focus the camera for each photo, a process that can be difficult given the generous depth-of-field digital cameras provide at most zoom and aperture settings. On the one hand, the extra depth-of-field makes the need for precise focus less necessary, but, on the other hand, when you want exact focus to ensure best results, you might find it difficult to achieve.
To make things even more interesting, some digital cameras have other parameters to choose from. The simplest of these are the focus ranges that can be set. These include:
- Autofocus. This range provides normal autofocus operation for the full automatic range of the camera, typically infinity down to a foot or less. Some cameras provide autofocus at even closer distances; if you'll be doing a lot of close-up work, you'll want to check this specification before you buy.
- Infinity range. This setting locks the focus setting for distant objects, such as landscape scenes or buildings. The advantage of this range is that the camera's autofocus feature is disabled, so there is less lag when you press the shutter release to take the picture.
- Macro/close-up range. This setting moves the lens elements so that the camera focuses much closer than in autofocus mode, frequently to less than one inch. With some cameras, autofocus still functions at these close distances, and you might be able to adjust the magnification of your image by zooming in and out. Other cameras function only in manual focus mode when set to the macro position. One of my cameras, for example, can be locked into macro mode at either the widest or longest zoom settings. At the wide-angle macro mode, the field of view is fixed, but focus can be adjusted with a focus ring around the lens. At the tele macro setting, the focus ring is still used, but the zoom ring can also be adjusted to provide small changes in magnification.
- Single area. With this mode, the camera focuses on the subject matter that is in the active focus area. This works best with static subjects that won't be moving while you compose your image.
- Dynamic area. With this mode, the camera focuses on the subject in the active focus area, but if that subject moves before the picture is taken, the camera automatically switches to the focus area now occupied by the subject. This is a good mode when the subject may move, but is relatively static.
- Closest Object focus. With this mode, the camera automatically focuses on the subject that is closest to the camera. If the subject moves, the camera shifts focus to that area. This mode is a good choice only if your main subject is, in fact, the closest object to the camera.
- Face Priority focus. This is a novel focus mode introduced by Nikon. The camera actually looks for faces in the frame and sets focus on the face that is closest to the camera.
- Predictive focus. If your subject is moving, predictive autofocus can set the focus distance to where the camera guesses that the subject will be at the time the photo is taken. This is especially good when your subject is approaching or retreating.
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