Zone Focusing - Point and shoot simplicity

Camera zone focusing is a technique to help you take pictures with more convenience, accuracy and speed. It uses depth of field controls to establish a zone of sharpness in which any subject can be photographed without further attention to focusing; these controls are coordinated by the depth of field scale built into most lens barrels. Let's study some example of zone focusing to better understand how it works.

Suppose you find yourself standing on the sidelines as a parade goes by. You have a 35mm camera and a 50mm lens. The day is bright and the sun is in the right direction. Everything seems ideal for effective photography. However, there is one problem - focusing. The parade is constantly moving, so the distance to any one person or things keeps changing. Besides that, when the high school bands or rows of horses and riders go past, the nearest person is only about 3m (10ft) away, but the farthest is about 15m (49ft) away. Is it possible to get both ends of a line sharp in the same picture? And if so, where do you focus to do it?

This is a typical situation in which zone focusing can make your life easier. The first thing to do is to consult your depth of field scale. If your ISO setting is low, and yet you require high shutter speeds to stop the parade action, you have been shooting been shooting at f/8. By placing the near distance you want sharp (3m, or 10ft) opposite f/8 on the scale and then checking the far distance against the other f/8 mark, you determine that the zone of sharpness extends only to about 8.5m (28ft). That is not enough! But by placing the f/11 mark opposite 3 meters (10 feet), you see that the far distance is now well beyond your requirements. Good- except that f/11 calls for shutter speeds that are too slow, so this solution is also unworkable.

The three prime factors controlling depth of field are focal length, aperture and distance. You can't change focal length, since you have only one lens with you. You have explored the possibilities of changing aperture without success. That leaves just distance to help you. You check your depth of field scale again and see that if your preferred f/8 lens stop is set against 5m (16 ft) as the near distance instead of 3m (10 ft), you have a zone of good focus from 5m almost to infinity. That's the answer! You change your position so that you are 5m from the nearest subject, keep your aperture at f/8 and set 5m opposite the f/8 mark on subject, keep your aperture at f/8 and set 5m opposite the f/8 mark on your depth scale, thereby selecting the point of focus automatically. Now without touching the focusing ring again, you can shoot picture after picture with ease and convenience knowing that everything of importance will be in focus.

Another situation calling for zone focusing might arise when you are taking a picture of your house with a 28mm wide angle lens. you want not only the house, but the tree in the yard and the white picket fence as well to be in focus. How can you make sure all these things will be sharp at once? From the position you have selected for the camera, the nearest part of the fence is only 1.8m (6 ft) way, while the far end of the house is more than 30m (100 ft) away. This range would be difficult for most normal lenses to handle, even at the smallest aperture, but a 28mm wide angle lens ahs more inherent depth of field. Checking the depth of field scale on the 28mm lens, you find that even at f/5.6, you can adjust the lens so that the zone of sharpness extends from about 1.8m (6 ft) to infinity - more than enough to ensure accurate coverage. At smaller stops, depth is even greater.

In situation calling for quick response in making an exposure, zone focusing is even more useful. Imagine yourself at a basketball game. You have brought a 135mm lens in order to get close up action at one of the baskets and the fast action. However, you want to avoid focusing every time something interesting occurs. Things will be happening too fast for that, and you will lose many good shots. Zone focusing is the answer.

Consulting the depth of field scale on your 135mm lens, you find (by trying various combinations) that setting 10m (30ft) opposite the f/11 mark on the short end of the scale produces 15m (50ft) on the long end. Armed with this information, you take a seat 10m from where the closest action will occur, set your lens at f/11, and set 10m against the f/11 mark on the depth scale. Now without touching the focusing ring, you can shoot action around the near basket as fast as you please, knowing you have 6m (20 ft) zone of sharpness in which to work.


More information about camera focusing

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