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Chapter 12 ■ Making Light Work for You 409
Figure 12.7
A focal plane
shutter has two
curtains, the
lower, or first
curtain, and an
upper, second
curtain.
When first-curtain sync is used, the flash is triggered at the instant that the sensor is com-
pletely exposed. The shutter then remains open for an additional length of time (from
30 seconds to 1/250th second), and the second curtain begins to move downward, cov-
ering the sensor once more. When second-curtain sync is activated, the flash is triggered
after the main exposure is over, just before the second curtain begins to move downward.
A Typical Electronic Flash Sequence
Here’s what happens when you take a photo using electronic flash, either the unit built
into the Nikon D7000 or an external flash like the Nikon SB-900, all within a few mil-
liseconds of time:
1. Sync mode. After you’ve selected a shooting mode, choose the flash sync option
available in that mode by holding down the Flash button and rotating the main
command dial until the icon representing the choice you want is displayed in the
top-panel monochrome LCD. (See Figure 12.8.)
2. Metering method. Choose the metering method you want, from Matrix, Center-
weighted, or Spot metering.
3. Activate flash. Press the flash pop-up button to flip up the built-in flash, if neces-
sary, or mount (or connect with a cable) an external flash and turn it on. A ready
light appears in the viewfinder and on the back of an external flash when the unit
is ready to take a picture.