5. TTL flash control
33
The mecablitz receives its information exclusively
from the connected TTL-controlled camera.
Exposure measurement in TTL mode (TTL =
t
hrough-
t
he-
l
ens) is completed by the camera’s sensor. This
sensor measures the light reaching the film through
the camera lens. An electronic control circuit within
the camera transmits a stop signal to the flashgun as
soon as the film has been exposed by the correct
amount of light; the flash is then instantly cut out. The
advantage of the TTL mode is that all factors
influencing the exposure of the film (such as filters,
change of aperture or variable aperture zooms) are
taken into account. You need not worry about adjust-
ment of the light output. The camera’s electronic
system automatically defines the required amount of
light. You can also utilize various metering facilities
(e.g. spot , matrix or centre-weighted overall readings)
offered by some cameras.
The maximum range for the selected aperture is
indicated underneath the f-stop on the aperture
calculator. Example: With ISO 100 and f/4 the
maximum flash range is 7 m (see fig. 3). The
minimum lighting distance equals approximately
15% of the maximum flash range.
If the actual distance is shorter than the
minimum lighting distance, then this may
result in overexposure.
A strip of film must be loaded in the camera if tests
are to be conducted in TTL flash mode. The effective
flash range can only be checked by the correct-expo-
sure display (o.k.) if the flash is triggered by the
camera and not with the manual release on the
flashgun!
k
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