300 THE HASSELBLAD MANUAL
Other lenses are focused to closer distances by physically moving the entire lens further
from the image plane. This reduces the amount of light reaching the image plane. The amount
is negligible for all practical purposes within the normal focusing range of a lens because it
practically never exceeds ½ f stop. Furthermore the loss is compensated for when exposure
is determined with a metering system in the camera.
Exposure Values
Exposure values (EVs) are seldom used, but it is worthwhile knowing that EVs are single num-
bers that indicate how much light exists in a certain location or is refl ected from a subject for
a specifi c fi lm sensitivity. A camera or lens set to a specifi c EV number produces the same
exposure at any aperture and shutter speed combination. (see Figure 16-1).
Figure 16-1 Exposure values. (1) A lower EV number indicates a smaller amount of light or a
darker subject. (2) If the EV is 17 for 400 ISO it will be 15 for ISO 100. (3) Most professional
exposure meters have an EV scale. (4) For every EV value you have a choice of various
aperture and shutter speed combinations, such as f/2.8 and
1
/
60
second or f/16 and ½ second.
Both give the same exposure because they have the same EV value.
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