On Jul 10, 2007, at 11:31 AM, Cotty wrote: > Can someone please give me a rundown on the difference between a > linear > and a circular polarizer? If you place a linear polarizer in front of > your lens and rotate it, will that alter the reflections etc like a > circular polarizer will?
from http://www.tiffen.com/polarizer_pics.htm : "... A Circular Polarizer is a linear one to which has been added,on the side facing the camera, a quarter wave retarder. This corkscrews the plane of polarization, effectively depolarizing it, eliminating the problem. The Circular Polarizer otherwise functions in the same manner." So ... What this means is that a circular polarizer is a linear polarizer with an additional element that makes it directional: light passing into the polarizer in the correct direction has been polarized regards the source (subject) but is depolarized as it approaches the target (film, sensor, etc) behind the filter. If you reversed the direction of light relative to the filter, the emitted output would be polarized. A linear polarizer is not directional: light passing through it is polarized in both directions. Circular polarizers were invented to prevent errors with camera sensor systems that are sensitive to polarized light due to other, natural polarizing elements ( mirrors, prisms, etc.) in the light path (like AF sensors, exposure meter sensors). Circular polarizers work exactly like a linear polarizer does in practice, although inexpensive ones prove to be a little less efficient in the degree of polarization they effect. Stacking circular polarizers can be done to create a ND filter much like you do with linear polarizers provided you reverse the frontmost polarizers relative it's normal orientation in operation. Godfrey -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
