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5.7.6 Pre-flash TTL and ADI metering (Sony)
These types of flash mode are used with Sony digital
cameras and adjusted on the camera.
During shooting, a measurement pre-flash is executed before
the actual exposure. The camera evaluates the measurement
pre-flash and controls the light output for the main flash. In
the case of ADI metering, additional distance data from the
lens is incorporated into the flash exposure process. The flash
unit automatically adapts itself to the mode selected on the
camera.
5.7.7 Manual TTL flash exposure correction
The TTL auto flash mode of most cameras is matched to a 25%
degree of light reflection by the subject (average amount of
light reflected by flash-shot subjects). Consequently, a dark
background that absorbs a great deal of light, or a bright
background that reflects a great deal of light, can result in
under- or overexposure, respectively.
To offset this effect a correction value can be set on some
90
cameras to manually match the TTL flash exposure to the
photographic situation. The actual extent of correction
depends on the contrast prevailing between subject and
background. The correction value is set on the camera.
Please refer to the camera's operating instructions for details
concerning the settings.
A dark subject in front of a bright background:
Positive correction value (approx. 1 to 2 EV).
Light subject in front of a dark background:
Negative correction value (approx. -1 to -2 EV).
Exposure correction by changing the lens diaphragm is not
possible because the camera's automatic exposure system
will automatically regard the changed diaphragm as the nor-
mal working aperture.
After the exposure do not forget to reset the TTL flash
exposure correction back to the normal value on the
camera!
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