P3D Rochwite Realist Polariser

[Steve Spicer <s.spicer@xxxxxxxxxxxxxxxxxx>]

>From Sell-3d:
>
> it has a near mint machined and anodized aluminum Rochwite ganged
>polarizing unit which can be flipped up or down as needed.
>

I had a chance to look at one of these a while back.
( http://home.mira.net/~kiewavly/rochwite.html ).
The 3 polarisers rotate in mechanical synchronism, but 
the maximum rotation was 90 degrees on the unit I looked at.

Why is 90 degrees adequate? I suppose it might be to do
with the polarising angles generated by skylight. My naive
understanding of the situation might have led me to think that
180 degrees rotation would be required to cover any possible
polarisation angle.

Steve Spicer
Australia
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