338 THE HASSELBLAD MANUAL
Dedicated Flash Exposures for Film and Digital Imaging
Although dedicated fl ash provides consistent exposures in the simplest possible way, there
are a few facts you must know and understand to obtain the best possible results.
The sensor in all Hasselblad dedicated fl ash cameras measures the light refl ected off a
40 mm center area of the image plane. The subjects that need to be properly exposed by the
fl ash must be in that center area, as is usually the case. This is seldom a problem because the
measuring area is rather large.
At present the Hasselblad dedicated fl ash systems are adjusted for the refl ectance value
of fi lm surfaces (OTF). There are slight differences in fi lms, but they are small and need not
be considered. Nevertheless, you may want to make your own test with the fi lm that you
are using. In digital imaging, the fl ash light is refl ected off the sensor which has a different
refl ectance value than fi lms. You need to make the recommended adjustment of 1
2
/
3
f stops
but evaluate the histogram carefully as sensors may differ and change. This compensation
is not required when using a Hasselblad digital back on the H camera. The camera adjusts
automatically for the difference in refl ectance values. This is discussed further a little later in
this chapter under Dedicated Flash in Digital Imaging.
Subject Color and Brightness
The fl ash sensor in a dedicated or automatic fl ash system is adjusted for 18% refl ectance and
produces perfect exposures only when the subject refl ects 18% of the light, as the colors in
the 0 column on the chart (Figure 15-6) in the exposure section do (see Figure 18-3). The
subject brightness must be considered if the subjects within the 40 mm fl ash metering circle
Figure 18-3 Flash tests. (1) The fl ash sensor in the camera is adjusted for 18% refl ectance. Bright
subjects turn the fl ash off earlier, creating underexposure; dark subject areas do the opposite.
(2) The new Hasselblad rear covers have a center area that refl ects the same amount of light
as the fi lm and can be used for checking whether fl ash illumination is suffi cient.
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