The Tiffen 138mm Self-Rotating UltraPol Circular Polarizer Filter is a mounted filter that includes rear and front threads that allow filter stacking when using third-party or custom filter holders. This filter's rear threads are intended to retain a 138mm non-self rotating mounted filter that is already placed within a compatible filter holder. A supplemental effect is then provided in addition to that of the retained filter. The Tiffen 138mm Self-Rotating UltraPol Circular Polarizer Filter's front threads can then accommodate an additional non-self rotating mounted filter, which can then be held in place with a 138mm retaining ring. Alternatively, another Tiffen 138mm self-rotating filter may be screwed on top of the Tiffen 138mm Self-Rotating UltraPol Circular Polarizer Filter.
Once installed, this filter helps to reduce reflections and glare by filtering out light that has become polarized due to reflection from a non-metallic surface. The light from the sun naturally becomes partially polarized due to reflecting off electrons in air molecules, causing the light to scatter into what appears as haze. A polarizing filter arranges, and filters, this directionally polarized light perpendicularly to the reflected light, allowing for the absorption of much of this light. This results in a noticeable reduction of glare and reflections from non-metallic surfaces and an increase in the saturation of skies and foliage.
A circular polarizer only differs from a linear polarizer in that it contains a quarter wave plane in addition to the linear polarizing filter. The addition of this quarter wave plane is to circularly polarize the 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, 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 non-coated, has approximately 40% average light transmission, and is designed to provide a polarization effect that is 15 to 20% greater than other Tiffen filters which only provide a linear or circular polarization effect and are not UltraPol filters.
The Tiffen 138mm Self-Rotating UltraPol Circular Polarizer Filter is constructed from Water White glass for increased clarity as well as color fidelity.