Nikon D7000 manual 141

Chapter 5 ■ Mastering Autofocus Options 141

5 ⋅ 7-inch print viewed at arm’s length, might appear blurry when blown up to 11 ⋅ 14 and examined at the same distance. Take a few steps back, however, and it may look sharp again.

To a lesser extent, the viewer also affects the apparent size of these circles of confusion. Some people see details better at a given distance and may perceive smaller circles of confusion than someone standing next to them. For the most part, however, such dif- ferences are small. Truly blurry images will look blurry to just about everyone under the same conditions.

Technically, there is just one plane within your picture area, parallel to the back of the camera (or sensor, in the case of a digital camera), that is in sharp focus. That’s the plane in which the points of the image are rendered as precise points. At every other plane in front of or behind the focus plane, the points show up as discs that range from slightly blurry to extremely blurry (see Figure 5.9). In practice, the discs in many of these planes will still be so small that we see them as points, and that’s where we get depth-of-field. Depth-of-field is just the range of planes that include discs that we perceive as points rather than blurred splotches. The size of this range increases as the aperture is reduced in size and is allocated roughly one-third in front of the plane of sharpest focus, and two-thirds behind it. The range of sharp focus is always greater behind your subject than in front of it.

Figure 5.9

Only the blos- soms in the foreground are in focus—the area behind them appears blurry because the depth-of- field is limited.