FMF - Friends of Minerals Forum, discussion and message board

[Dean Allum]

Duncan,

I created that setup and saw 4-extinctions per 360 degree rotation when the Z-axis was perpendicular to the light. This setup does not appear to work if the surface is frosted or there are excessive internal ghosts.

When you place thin sections of mica between the polarizers, you get a Psychedelic Party!!!

I am going to put this onto an overhead projector for the next rock talk that I give to an elementary school. I am also wondering what this would look like with those orthogonal polarized lenses now used in 3-D theaters.

Thanks,
Dean Allum

[Duncan Miller]

Dean

See Olaf Medenbach's superb web site <homepage> for ideas about working with polarized light and crystals. Go to "How to play with polarized light", download the file, and save it for future use. He explains how to you use a flat screen monitor or cell phone as a source of plane polarized light. Most overhead projector lamps are not bright enough but you can use an ordinary slide projector (if you can find one) as a light source for demonstrations. I haven't tried using a digital data projector and don't know their polarization characteristics.

My understanding is that the REALD 3D spectacles used in most movies operate with circularly polarized light. You can get paradoxical effects if they aren't orientated correctly. Try using them mutually reversed to obtain extinction. This is because the plane polarizing filter has an incorporated 1/4 wave plate on one side (as explained on Olaf's site), which converts plane to circular polarization, and vice versa if the right way around.

Duncan