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5.7.4. TTL flash mode with measurement pre-flash
function (Olympus)
During the shot and before the actual exposure, one or
more pre-flashes are executed by the flash unit. The camera
evaluates the measurement pre-flash and controls the light
output of the flash unit for the main flash.
The flash unit is set to this mode by the camera automatically.
5.7.5. P-TTL flash mode (Pentax)
With P-TTL flash mode a measuring pre-flash is fired before
the actual exposure. The camera evaluates the measure-
ment pre-flash and controls the light output for the main
flash.
The flash unit is set to this mode by the camera automatically.
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 befo-
re the actual exposure. The camera evaluates the measure-
ment 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 selec-
ted 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
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
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