5. TTL flash control
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The mecablitz receives its information exclusively
from the connected TTL-controlled camera.
Exposure measurement in TTL mode (TTL = through-
the-lens) 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 influen-
cing the exposure of the film (such as filters, change
of aperture or variable aperture zooms) are taken into
account. You need not worry about adjustment of the
light output.The camera’s electronic system automa-
tically 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.
The speed of films to be exposed under TTL
flash control must be between ISO 25/15°*
and ISO 1000/31°. Correct exposures cannot
be guaranteed with other film speeds.
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-exposure
display (o.k.) if the flash is triggered by the camera
and not with the manual release on the flashgun!
*
With automatic film speed setting (DX): ISO 32/16°
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