对焦选择(hyperfocal focusing).doc

Hyperfocal Focusing
When should you use hyperfocal focusing? Well, sometimes when shooting a landscape, you want everything sharp from the front to the back of the scene. Setting a small aperture such as f/16, f/22 or even f/32 can help, but if you really want to maximze depth of field, hyperfocal focusing is the technique you need to use.
To do this, you need a camera where you can switch to manual focusing and a lens inscribed with a depth of field scale (not all modern lenses have these markings these days, especially zoom lenses). If you're not familiar with these kinds of lens markings, here's a quick explanation:
Lens Markings Primer
The picture below of a typical lens (in this case a 28mm) shows four sets of markings. At top is the distance scale (on the lens' focus barrel) showing figures in feet and meters (this also shows the infinity position).
Below that are a set of lines beneath which are the f-stops of the lens. This is the depth of field scale. For each f-stop, there are two equidistant marks, one to the left and one to the right of the central mark on the scale.
The bottom set of figures shows the selected f-stop for the lens. These are on the lens aperture ring and, as you change the aperture, the selected f-stop under the central line on the depth of field scale will tell you what aperture you've selected.
To find out what part of a scene is in focus is simply a matter of reading the distance scales between the two marks for your selected f-stop on the depth of field scale. For example, let's say I've focused on something that's 3 feet away. If my lens is set at f/, then reading the distance values at the two "" marks on the lens shows that everything just shy of 3 feet to about feet will be in focus (a little guesstimation is required in reading the distances). This is fine for isolating your subject from everything else.
If I close the lens down to f/11, then reading the distances for the two "11" marks shows that everyth