A circular polarizer consists of two layers. One normal polarizing layer in
front and a 'depolarizer' on the back side. This makes sure that a
polarization-sensitive system behind the filter (a photosensor behind an OM
2s/3/4(Ti) mirror) doesnt get fooled by polarized light. If a circular
polarizer is turned around all polarized light (f.i. reflected from the sky)
gets depolarized first and filtered later. The same amount of polarized
light comes through the filter, whatever direction the filter is turned.
The strange thing is that natural light gets polarized all the time. Light
from the 'nice and blue sky' _is_ mostly polarized (depending on the
location of the sun). This would mean that our OM 2s/3/4(Ti)'s do get fooled
even without the use of a linear polarizer! Experiment: Manual exposure, one
picture from a nice and blue part the sky (only the sky!) in portrait format
and another picture in landscape format. Do the indicated exposures change?
Daan
Pictures of Insects at:
http://www.kalmeijer.net
> If the sky's nice and blue where you are you can easily find out - a
> linear polarizer has the same effect on the sky (and any other polarized
> light source) whichever side you look through, but a circular polarizer
> will only work from one direction. Strange but true!
>
> Roger
>
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