Nikon D7000 manual Stops and Shutter Speeds

Chapter 4 ■ Getting the Right Exposure 99

■Light captured by the sensor. Not all the light falling onto the sensor is captured. If the number of photons reaching a particular photosite doesn’t pass a set thresh- old, no information is recorded. Similarly, if too much light illuminates a pixel in the sensor, then the excess isn’t recorded or, worse, spills over to contaminate adja- cent pixels. We can modify the minimum and maximum number of pixels that con- tribute to image detail by adjusting the ISO setting. At higher ISOs, the incoming light is amplified to boost the effective sensitivity of the sensor.

Figure 4.3

Top row (left to right): f/2, f/2.8, f/4, f/5.6; bottom row, f/8, f/11, f/16, f/22.

F/STOPS AND SHUTTER SPEEDS

If you’re really new to more advanced cameras (and I realize that some ambitious ama- teurs do purchase the D7000 as their first digital SLR), you might need to know that the lens aperture, or f/stop, is a ratio, much like a fraction, which is why f/2 is larger than f/4, just as 1/2 is larger than 1/4. However, f/2 is actually four times as large as f/4. (If you remember your high-school geometry, you’ll know that to double the area of a circle, you multiply its diameter by the square root of two: 1.4.)

Lenses are usually marked with intermediate f/stops that represent a size that’s twice as much/half as much as the previous aperture. So, a lens might be marked: f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, with each larger number representing an aperture that admits half as much light as the one before, as shown in Figure 4.3.

Shutter speeds are actual fractions (of a second), but the numerator is omitted, so that 60, 125, 250, 500, 1,000, and so forth represent 1/60th, 1/125th, 1/250th, 1/500th, and 1/1,000th second. To avoid confusion, Nikon uses quotation marks to signify longer exposures: 2", 2"5, 4", and so forth representing 2.0, 2.5, and 4.0-second exposures, respectively.