105mm screw-in glass circular polarising filter which saturates colours and deepens blue skies, and reduces reflections off water and glass. A Circular (as opposed to Linear) Polariser is required by all autofocus cameras, and some manual focus cameras using beam splitters in their metering systems. It can also be used on any manual focus camera with exactly the same results. The advantage of a 105mm round polariser over the square 100mm type produced by Lee is that it can be used with the standard Foundation Kit holder and graduated filters. To use grads with the square type the Professional Kit is required, in order to allow independent rotation of both polariser and grad. As a result the greater extension of the Pro Kit in front of the lens severely limits use with wide angle lenses. The 105mm polariser fits to the front of the holder by means of the 105mm Polariser Adaptor Ring (extra).