Nikon D300 Complete Manual page 605

modes, Auto Aperture (ÊÊ), Automatic (Ê), and Manual (Ë)
flash, differ in that the flash performs much of the flash
exposure calculation and the camera body does not
determine when the flash shuts off:
Auto Aperture (ÊÊ): Unique to digital camera bodies using
external SB-800 flashes. In Auto Aperture flash mode the
Speedlight obtains the ISO value and aperture being used
from the camera, as well as the signal to start the flash (i.e.
"shutter's open, go ahead"). Like i-TTL modes, Auto Aperture
flash mode fires a preflash, I believe to help the metering
system refrain from blowing out highlights when the flash is
fired. During the exposure, a sensor on the front of the flash is
monitored, and when the amount of light that sensor sees
reaches the level the flash calculates it needs, the flash stops
firing. This mode is not available on the D300 except with the
SB-800, and appears to be one of the simplifications Nikon
made from the pro series cameras.
Automatic (Ê): Available with all external flash units that
have an Automatic flash mode. In Automatic flash mode, the
Speedlight usually
preflash is fired). You must transfer the aperture and ISO used
on the camera by setting this manually on the flash. Again, a
sensor on the front of the flash is monitored, and when the
amount of light it sees reaches the level the flash calculates it
needs (based upon aperture setting and ISO value), the flash
stops firing. Besides the cumbersome limitation of transferring
the aperture and ISO settings to the flash, the flash sensor
doesn't see the same thing as the camera lens, which can
result in errant flash levels.
Note: The classic "trouble case" for both Automatic and Auto
Aperture flash modes is shooting through a doorway: the
flash sensor sees light reflecting off the door frame and
nearby walls, while the lens may be zoomed in to only see a
146 Most older Speedlights and third-party flashes do not communicate anything with
the camera and only understand the "fire now" signal.
Thom Hogan's Complete Guide to the Nikon D300
146
sees only the signal to start the flash (no
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