Figure 1-5. Effect of polarizing screen
10.
How to use polarizing screens.
a. Polarizing filters are often used to control sky brightness because they reduce the polarized
light reflected from the sky. Polarizing filters are most effective for controlling sky brightness when the
sun is at a right angle to the optical axis and least effective when the camera is looking into or away from
the sun.
b. When you photograph through water, acetate, or glass, use a polarizing screen. Place the
illumination at an angle of 30 degrees off the surface of the water, acetate, or glass.
c. Just as you turn the coin until it fits into the slot, you must rotate the polarizing screen until it
blocks the polarized light. If you use polarizing material over your light source or if you use a filter over
your lens, look at the scene as the camera will see it while you rotate the filter for the desired effect.
11.
Polarizing screens decrease exposure.
a. A polarizing screen decreases the amount of light that gets to the film; it not only blocks
polarized light but also reduces the intensity of unpolarized light.
b. Polarizing filters reduce light about 2.5 times, however, a definite factor cannot be applied. It
is best to experiment with the filter you are using in order to estimate the filter factor.
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