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True Exposure is an HC/HCD lens function that allows the
shutter speed to remain un-affected when stopping down.
This effect is perhaps not so commonly understood as it is
restricted specifically to integral lens shutters as opposed to
focal plane shutters.
When a lens is stopped down, the effective shutter speed
becomes longer, consequently affecting the set exposure. At
slow shutter speeds the effect is minimal but at faster speeds,
e.g. 1/500s, the effect becomes clearly visible. As Hasselblad
knows exactly how the shutters behave in HC lenses, auto-
matic compensatory measures in speed setting adjustments
are therefore employed.
As compensation can only be put into effect where speeds
can be adjusted, this prevents the possibility of adjusting the
fastest speed of 1/800s. To counter this, compensatory adjust-
ments are therefore made to the aperture instead to retain
the set exposure.
Note
You can download a fuller ex-
planation of this situation from
www. hasselblad.com.
TRUE EXPOSURE
Light level at
image plane
T fully open
T stopped down = T fully open
(using True Exposure)
T stopped down > T fully open
(without True Exposure)
Time
Maximum aperture
Stopped down one stop with True Exposure mode ON
Stopped down one stop with True Exposure mode OFF
However, this compensation is not always required and
when using flash/strobe as the main light source it is actually
undesirable because compensation will result in underex-
posure. Therefore, when using flash/strobe as the main light
source, you should set True Exposure to OFF in Custom
Options #13 on grip.