The last article began a discussion of ISO, shutter speed and F-stop settings. The F-stop, or size of the lens opening, sets up another consideration, besides shutter speed, and that is depth of field. Depth of field, very simply, is the distance from the lens that will be in focus. It’s actually pretty basic physics. To understand depth of field, try this: line up two objects, one 15-18 inches away, the second 30-40 feet away. Close one eye and focus your eye on the closer object; the distant object will appear blurry in your peripheral vision. Now focus on the distant object; the closer object appears blurry. In real life, our mind is fast enough to make both objects seem in focus at the same time because we’ll tend to focus on the object that were thinking of, but the camera isn’t smart enough to do this – yet (they’re working on it). With any particular F-stop setting, the point of focus should be sharp and, in focus - there will be a distance from in front to behind the point of focus that will be acceptably in focus when printed; the farther away from the point of focus, the more out-of-focus and blurry those parts of the photo will become. Generally, the higher the F-stop, the greater the depth of field.[Illustration 005-1]
When using the pre-sets (modes) on your camera, your camera will set for distinct priorities. Portrait settings will aim for shorter depth of field or lower F-stop; Landscape will aim for maximum depth of field or higher F-stop. Sports photos will generally use shorter depth of field, faster shutter speed and flash to stop the motion; without flash, you’ll need a shutter speed of at least 1/400 sec or faster to stop the action; with flash, you’ll have to be close so the flash can effectively light your subject – especially with a consumer level camera where the built-in flash may not project very far. Night time setting will generally need a more open F-stop and higher ISO; because of slower shutter speed, a tripod will be very helpful.
These are general settings and can’t accommodate all possibilities. The settings modes are programmed to help consumers who may not take 4000 pictures per week get acceptably good photos easily as possible. You may need to change some of the menu settings (if at all possible) to handle other photo conditions. When in doubt, you can always resort to the Auto mode; I’ll admit it; I use it occasionally.
As you get into more expensive cameras and features, you may also have a shutter-priority mode, an aperture-priority mode, a manual mode and a bulb mode. In the priority modes, the shutter or aperture can be manually set and the camera calculates the rest for a good exposure (ISO settings may be automatic or manually set, depending on the camera and menu settings). [Illustration 005-2] When you get into more specific applications, if you were to ask five professional photographers how they would set their camera, you could possibly get five different responses. That’s not to say one is right and four are wrong, but rather this is what works for that person with their equipment and in that lighting situation.
If you’re using flash, a variant of depth of field also affects lighting. We’ve all experienced a flash photo where the subject is well lighted, but the background is very dark. Or how about a group photo where the front row or center is overexposed and the pict is increasingly underexposed as the distance from the focus point increased? When you use flash, the camera calculates how much flash intensity will be needed to light the point that the camera focuses on; anything closer will be overexposed; anything farther away will be underexposed. The flash intensity will decrease with the square of the increased distance. Simple physics again: doubling the distance means only ¼ as much flash lighting. For example, if the distance to subject is 4 feet and the distance to background is 8 feet, the background will get ¼ as much light as the subject. This decrease in lighting translates to about one F-stop. Possible solutions? Turn on every light that you can, use a slave strobe to help light the parts farther from the camera, or get farther away from your subject and use a telephoto lens. Why? – that’s the subject for another article.
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Tip #1: The faster the movement of your subject, the faster your shutter speed must be to capture the picture without motion blur. Even in daylight, you may choose to use flash to help freeze the motion.
Tip #2: Short depth of field in portrait photos will focus the viewer’s attention on the subject of the photo by blurring other objects in the photo.
Tip #3: Try to keep your backgrounds uncluttered or intentionally blur them by using depth of field. [Illustration 005-3]
Tip #4: When possible, many professional photographers prefer to use natural lighting; if that’s not possible, they’ll try to set lights to approximate the natural lighting.
Next article: answering reader’s questions: 1) Landscape vs.Portrait, 2) What camera supplies should I take on a trip? |
