Stefan Gerris wrote: > Physically speaking there is no circular polarisation envolved > whatsoever!
The light behind the circular polariser is circularly polarised. > I love to figure out how stuff works. In the past I've submitted some comments on circular polarisers to the list, but it seems that the mailing list archives are offline at the moment. Some parts are reproduced below. Feel free to ask for further clarification if this is not clear enough. > this polariser on wider angle zooms The polarisation of the sky depends on the angle with the sun. Thus you often get uneven brightness in the sky if you use polarisers with wide angle shots. Regards, Peter Wagemans -------------------- March 1999: A circular polariser first polarises the light linearly and then converts it to circularly polarised light. Linear polarisation means that the oscillation occurs only in one direction perpendicular to the light ray. At a fixed point illuminated by this light, the oscillation can be viewed as an arrow whose endpoint goes up and down along a fixed direction perpendicular to the light ray (the endpoint goes zero, positive, zero, negative, ...). At a fixed point, circularly polarised light has a arrow of constant length rotating in the plane perpendicular to the light ray. The conversion of linear to circular polarised light is performed by a thin layer of special material in which the speed of light in one direction 45 degrees from the direction of the linear polarisation is slightly different from the speed in the perpendicular direction. The initially linearly polarised light can be viewed as two arrows along those 45 degree directions oscillating up and down at the same time (in phase). While these two parts propagate through the special material, one falls behind the other. The thickness of the layer is such that on exit one part is a quarter oscillation behind the other one. Thus on exit from the layer, there are two arrows oscillating out of phase by a quarter oscillation. Adding these two arrows results in an arrow of constant length that rotates: circularly polarised light. -------------------- Feb 2002: A circular polariser is a linear polariser followed by a 1/4 wave plate. The 1/4 wave plate splits the linearly polarised light into two components at 45 degree angles to the linear polarisation. Initially these components oscillate in phase. Due to different light speeds of the two components in the 1/4 wave plate, the two components are 1/4 period out of phase when they exit the plate. This makes circularly polarised light. It's like the horizontal and vertical position component of some point on the rim of a vertical rotating wheel: the horizontal and vertical positions both oscillate with equal amplitude but 1/4 of the rotation period out of phase. Their sum corresponds to a circular motion. At a fixed point in space behind a circular polariser, the electromagnetic fields that describe light rotate in a plane perpendicular to the direction of the light (that's why it's called a circular polariser). -------------------- * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
