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Flash Control 153

5.10 FLASH CONTROL

Menu Position MENU  2  Flash Control

What it Does Allows you to choose between Pre-Flash TTL and ADI Flash
rd
Exposure Mode. There’s also a 3 option; “Manual Flash” where the output
of the flash is a fixed burst

Recommended Setting ADI
The ADI and Pre-flash TTL settings are very similar, so before I talk about
the differences let’s briefly discuss how the camera decides on the amount
of light to output for each shot it takes.
Once the camera has focused on the
subject and the shutter release button
has been pressed, the camera’s flash
first outputs a very low-level “pre-
flash” and then measures how much
light bounces off the subject and
back to the camera. The camera uses
this measurement to calculate the
proper amount of light to output, and
then a fraction of a second later, it
dispenses just the right amount of
light, based on the measurements of
the pre-flash. Since the pre-flash
light must pass through the lens
before it can be measured, this
method is referred to as “TTL” (for
“Through The Lens”). The great
advantage of TTL is that it will
calculate the right exposure
regardless of whether you have
filters in front of the lens, or you are Figure 5-20: ADI at work. ADI helps to
zoomed in all the way (changing the expose the subject properly in
maximum f/stop of the lens), or you situations where the background is too
are bouncing the flash off the ceiling. reflective.