No Subject

[Peter Homer <P.J.Homer@xxxxxxxxxxxxx>]

Michael Kentrox wrote in reply to a previous post.


> What's the difference, and forgive me, I am not sure I understand what you
> mean. Are you referring to a circular polarizer as in circular shape or a
> circular polarizer as in a linear polarizer with the combined retarder to
> make it a circular polarizer - a specific kind of polarizer filter.

A filter that does circular polarization.  I understand these are made
for cameras nowdays because linear polarized ones can cause problems
with modern camera operation (don't recall if it was with autofocus
or fancy metering schemes).

I have no idea if it'd be as effective to get the "polarizer effect"
inasmuch I've not used the circulars before, only the linears (and then
only in 2D).  However it'd solve the problem of buying small sized filters
(for price) and having to turn them in precise unison -- they'd only have to
be mounted whichever way and left stationary.  Probably couldn't get them
in series V format however.  :-(


I have not used circular polarisers either but it seems to me that they
would still have to be turned and in precise unison for stereo work. The
polarisation in the scene that you wish to eliminate is plane polarisation
and the filter would need to be rotated so that the two transmission
directions in the 1/4 wave retarder are at 45 degrees to it.So that it
splits into two components and the one is retarded 1/4 wavelength with
respect to the other which is what converts it to circular polarisation.
There must then be a second polariser of opposite circular polarisation to
block it. The point of this is that fancy metering systems have optics
which divert some of the light to the meter and beamsplitters which work by
reflecting/transmitting light also polarise it some degree and if it is
already plane polarised this tends to mess them up. All that happens to
circular polarisation on reflection is that the direction of rotation
changes.
               P.J.Homer



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