[Martin K]

Hi,
The circular polarizer is actually a linear polarizer combined with a retarder plate to ensure that the light wave emerges out of the polarizer in a "circular" way, i.e. unpolarized. So you first polarize the light to get rid of unwanted reflections, and then de-polarize it again. Otherwise the light measurement of the Leica SLR and R cameras will give the wrong result due to further polarizing action of the semitransparent mirror that syphons off some light for measurement. The yellow dot identifies the back of the polarizer, should therefore always be facing the film plane. Regards, Martin