Re: [Leica] use of circular polarizer

[George Huczek <ghuczek@sk.sympatico.ca>]

>>i have always thought that by turning this filter one would obtain different
>>density at different settings. it seems that my P-cir 13406 has an even
>>density across the entire filter even though the glass element can be
>>turned.
>>are my eyes getting bad ? If not, why can the glass be turned when the
>>entire glass has the same density /shading of grey ?
>
>The extent that light is polarized depends on the angle of the light.  You
>will have to look through the filter with the light coming in at an angle.
>That's why polarizing filters have more of an effect when the sun is low in
>the sky.  Take the filter outside on a sunny day and look at the sky
>through it from different angles.  As you turn the filter, you will see the
>sky darken when the light is most polarized.  Hope this helps.  Tina

This doesn't quite get to the point.  With a linear polarizer there is a
noticeable difference in the polarizing effect when the filter is rotated,
viewing at the correct angle of the sun as Tina mentions.  Take off the
linear polarizer, replace it with a circular polarizer, and rotate it at
exactly the same subject, and the extent of the difference in polarization
seems to be less noticeable.  I have noticed this effect as well and
wondered about it.
   Hans, I have no idea why this happens, but it does.  Your observation is
correct, and your eyes are not failing you.  The answer probably lies in
understanding the difference between linear and circular polarized light.
For that, stay tuned.  There are likely some LUGers out there who have a
better understanding of physical optics who might like to take a shot at
the answer.

- -GH