P3D Re: Round or Circular (polarizers)

["James R. Motley" <jmotley3d@xxxxxxxxxxxxx>]

On Oct 16, Boris wrote:

>>From: Rob <lilindn@xxxxxxxxxxx>
...
>>    There is a lot on confusion today about the two kinds of polarizers
>>now on the market - Linear polarizers (before about 1980 merely called
>>polarizers) and Circular polarizers.  Both usually come in round frames.
>...   [then, on "circular polarizers"]:
>>These filters to nothing of the sort.  A circular-polarized filter is
>>actually a linear polarizer with a quarterplate (a depolarizing layer)
>>behind it.  Perhaps a more correct term would be >>"polarizer-depolarizer

>I'm glad someone finally answered Bob's question in a manner that makes
>sense to me.  Learned something about polarizers today!  I love P3D!

>Boris Starosta            boris@xxxxxxxxxxxx
                          
I concur with Boris that Rob' explanation was excellent.  I especially
liked the fact that Rob included the following example to show how
anyone could see for him/herself the effect of the two types of
polarizers:

>> If you have a circular polarizer and a linear polarizer, try this
>>experiment: First, hold the linear between you and a light source.  >>Now, place the circular between your eyes and the linear filter and >>turn either filter.  You will observe that the light can be almost >>completely blocked out.  This is because the light is being polarized >>in one direction by the linear filter, and can't pass through the >>polarizing layer at the front of the circular polarizer - there's no >>light left the quarterplate layer to depolarize.  Now, hold the >>circular between you and the light, and place the linear between you >>and the circular. You will see that the light can only partially be >>blocked by turning the filter.  This is because the circular filter is >>polarizing the light, but then depolarizing it, and the linear filter >>can't completely block the light because it is not strongly polarized.
    
Thanks Rob--good job.  Now I have to go try this.

Jim Motley


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