A linear polarizer differs from a circular polarizer in that it does not contain an additional quarter wave plane. The addition of a quarter wave plane is to circularly polarize linearly polarized light for the use of auto focus and exposure functions. Due to how the light is broken down and filtered with a linear polarizer, in-camera auto focus and exposure accuracy become skewed during use. When the light becomes circularly polarized, it permits the use of these functions.
This filter is recommended when not using in-camera exposure metering or autofocus. It is non-coated and delivers approximately 40% average light transmission.
Tiffen filters are made using ColorCore technology; a process that involves laminating the filter substrate between 2 pieces of optical glass and grinding flat to a tolerance of 1/10,000th of an inch.