In article , PCA Cala <PCACala@xxxxxxx> writes
>Hi all:
>
>When using polarizing filters, DON'T change the exposure in relation to the
>polarizing effect! If you don't believe me, here is what Ansel Adams had to
>say (Adams, A. 1981. The Negative. New York Graphic Society, Boston, MA p.
>114):
>
>"Because of the change in values as the polarizer is rotated, photographers
>frequently assume the exposure factor must be increased as the degree of
>polarization increases. This is note the case! When used at the non-
>polarizing angle, the polarizer acts as a neutral density filter with a factor
>of about 2.5; at maximum polarization the same factor applies. If we
>increased the factor as the degree of polarization increased, the non-
>polarized areas would be overexposed."
>
>In "OM craft," one must meter in manual with the polarizer in a non-polarizing
>position, then rotate the polarizer to the effect desired and shoot at the
>settings previously determined.
>
All very nice in theory, Gary, and in Ansel Adams field I am quite sure
it worked very well since the main source of polarisation was the sunlit
sky. There are however, many cases where there are several sources of
polarisation at differing angles and in such conditions it is not
possible to meter at a 'non-polarising angle'. One example might be a
shot across a lake - at one angle the sky is darkened, but the lake
surface is quite reflective, whilst at another angle the sky is lighter
but the lake surface is non reflective. Other examples include any
scene with a lot of glass - such as modern city-scapes : it is almost
impossible to get an angle at which no cross polarisation of the
reflections occurs.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)
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