Flash-Differences between TTL and ADI


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ninelives

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Jan 16, 2002
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For those who interested in "Minolta-TTL and ADI".

Infos are provided by twm47099 in yahoo group.

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TTL (on the 7): You AF. The camera uses one of the AF sensors. It
selects the flash meter segment that corresponds to that AF sensor
and gives that higher weight in its exposure calcs. The shutter
opens. At the proper sync point the flash fires. The light from the
flash bounces off the subject, returns through the lens (TTL),
bounces off the film and hits the flash meter (in the mirror box
region). When the camera detects that the proper exposure has been
acheived it cuts off the flash.

ADI: You focus. The "D" lens tells the camera how far the subject
is. The camera tells the flash (lets use the built in flash for
simplicity) what guide number (power) to use to put the right amount
of light on the subject based on film ISO, aperture, distance. The
flash fires and theoretically should turn off at the correct exposure
without any TTL metering. This should be more accurate than TTL
since TTL is affected by the subject and background reflectivity.
However, whether Minolta uses some TTL when using ADI was the recent
subject of some controversy. Likewise with the 3600 and 5600 ADI
seems to require preflash. There was again argument about why that
was necessary or not. (Possibly to calibrate the guide number of an
add on flash?? Possibly to vote on the correct exposure --like the
space shuttle computers???) Minolta's not telling.

Tom

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