Use of filters
When light is measured through the lens
the energy reduction owing to filters is
generally allowed for automatically. But
the various films have different sensi-
tivities in the various spectral regions.
Deviations from the measured exposure
value can therefore occur with dense and
extreme filters.
Thus an orange filter, for instance, re-
quires an increase by about 1 stop value,
red filters on average about 2 stop
values. A completely accurate value
cannot be given since the red sensitivity
of black-and-white films varies a great
deal.
With circular-polarizing filters as supplied
with our lenses measurement and
settings can be carried out as with
ordinary filters. With ordinary polarizing
filters without circular effect the longest
exposure is determined by rotation of the
filter and set; now the desired effect is
found and the exposure made.
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