What is the difference between a Linear & Circular polarizer ?
A. There is no difference in the effect on the final image. The difference is in the technical way that the filter manages the light at wavelength level. Linear polarizers provide standard polarized light with all lightwaves vibrating in the same plane, whereas circular polarizers will polarize and then spin the lightwaves. The internal optics that control focussing or metering in some modern cameras cannot work with standard polarized light and therefore a circular polarizer is required. The information on which type is needed can normally be found in the instruction book for your camera.
