"Particularly with the pol filter it makes exact calculation almost impossible, as the exposure correction depends on how much you turn it. "
According to Ansel Adams this is incorrect, the filter factor remains the same regardless of the amount of polarized light.
"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 not the case. When used at the nonpolarizing angle the polarizer acts as a neutral density filter with a factor of about 2.5; at maximum polarizaiont the same factor applies. If we increased the factor as the deggree of polarization increase the non-polarized areas would be overexposed. The same factor applies regardless of the film or the light source." Adams, "The Negative," p. 114.
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