Hasselblad H2F User Manual

Also see for H2F -: Datasheet User manual

Contents

Hasselblad H2F User Manual Manual pdf 78 page image

78True exposureTrue exposureThe effective shutter speed for a central lens shutter is defined asthe length of time between the opening and closing when measuredat the half height position when expressed in diagram form (seediagram). The fact that it will take some time to open and closethe shutter will have an influence on the effective shutter speed asthe lens aperture closes to its setting. The faster the shutter opensand closes, the less this influence will be. It is also follows that theinfluence will be greater on shorter shutter speeds.With the lens at full aperture (largest opening), the amount oflight at the film plane appears as illustrated by the blue curve inthe diagram. The effective shutter speed then becomes T1. If thelens is now closed down by one stop, the amount of light appearsas illustrated by the red dashed curve. The effective shutter speedis now increased to T2, which is longer that T1. The result is thatthe exposure is not reduced by exactly one stop (1EV), however,but slightly less. At the shorter shutter speeds, the exposure errorcan be as much as 0,5 – 0,8 EV.The True exposure mode can compensate for this exposure errorsince the behaviour of the shutter is a known and predictable factor.At shutter speeds of 1/150 second or shorter (faster), the camerawill shorten the shutter speed to compensate, as illustrated bythe green dashed curve. At the fastest shutter speeds, however, itis not possible to adjust the shutter speed and so the aperture isadjusted instead.Although it is probably an infrequently used combination, pleasenote nevertheless that the fastest shutter speed / minimum aperturecombination cannot be adjusted by True exposure.T1T3 = T1T2Shutter positionTimeOpenClosedExposure at max aperture (e.g. f/2,8)Exposure at aperture f/4Exposure at aperture f/4 adjusted with true exposureShutter positionOpenClosedTimeExposure at max aperture (e.g. f/2.8)Exposure at aperture f/4Exposure at aperture f/4 adjusted with true exposure