Re: [Leica] Polas

["Henning J. Wulff" <henningw@archiphoto.com>]

At 8:26 AM +1100 11/4/99, Alastair Firkin wrote:
>Can now one help me ;-) How can I tell if my old pola is a circular type,
>and how using it on the R8 would affect performance?

If you have two polarizers, it's easy. If you have one filter which you
know is a linear polarizer, hold it up with the unknown filter between your
eye and the linear one. Turn the filters w.r.t. each other. If there is
only a slight shift in tone (warmer to cooler) then the unknown one is a
circular polarizer, and it has the side that has to face the lens facing
the linear pol filter. THIS IS IMPORTANT. Turn the unknown filter around,
and now the one position will be the normal gray and the position 90
degrees from that will be very dark.

If you have two filters of unknown type, different things can happen. Look
through both at once, and turn one w.r.t. the other. It should go black (or
_very_ dark blue-gray) at 90 degrees from the position where it should be
only about what you would expect from two gray filters if both are linear
polarizers or _OR_ if both are circular polarizers and the image side of
the filters face each other _OR_ if one is a linear polarizer and the other
a circular polarizer and the image side of the circular polarizer faces the
linear polarizer. If you have two circular polarizers and the camera sides
of the polarizers face each other, it is always very dark through the two
of them. If you have two linear polarizers, it doesn't matter how you
arrange the two of them, it will always be _very_ dark at 90 degrees from
the position where it's about as dark as you would expect from two gray
filters. Other combinations

If you don't have another polarizer, look at the reflection of a light,
that is coming off a non-metallic surface at about 30 degrees off the
horizontal. Turn the filter. Does the reflection dim?. Try looking through
the filter in the other direction. If the reflection dims in the same way
in both filter positions, you have a linear filter. If the reflection dims
in one position, but not if you look through the filter in the other
direction, you have a circular filter. The side that has to go towards the
lens is the side facing you when you had the filter in the position that
showed the dimming of the reflection.

If this starts sounding confusing, just read the first paragraph, and do it
that way.

   *            Henning J. Wulff
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