Maybe somebody out there can clear this up for me. Several years ago I remember reading a warning about the over use of polarizers at high altitudes. The writed claimed that at high altitudes (8,000+ feet) light is naturally polarized and the use of a polarizer can lead to unnaturally dark skies. He also claimed that this natural polarization was the reason many wide angle scenics shot at high altitudes showed vignetting at the corners since the polarization reduced the light coming in at the edges of the lens. <p> Any truth to this?