Lately we’ve been getting a bunch of questions on 4.5″ polarizing filters. There are several variations which can get quite confusing for those that are not familiar with them.
So here’s a rundown on the essential parameters:
4.5 inch is in fact the same as 114mm. Different manufacturers use metric or imperial. Likewise, some manufacturers refer to 138mm as 5.5 inch. These are both round filters.
Mechanically, there are a few physical variations:
Drop-in: A thin metal band that wraps the edge of the filter. This is the type fits into a mattebox round filter holder such as the MMB-1 bellows stage.
Threaded: A round threaded filter is one that is designed to screw directly onto a lens or sunshade. It will not fit in a mattebox.
Self-rotating: This is a common variant on threaded filters which is a two-stage unit. One part threads onto the lens and then the other stage rotates with the filter within for proper orientation. This type is generally much thicker than the others and definitely is not for use in a mattebox.
Unmounted: Generally not for direct sale. We use these filters to fit into our Rota-Pola trays. We sell a 4×5.65 tray with a 4.5″ polarizer mounted within on a geared wheel to orient its rotation. The special-order unmounted polarizer is used for this.
Optically we have numerous options as well:
Linear: This is the standard basic polarizing filter. Good for most applications.
Circular: Nothing to do with being physically round or not in shape. A circular pola includes a reversing or retarding layer which corrects for interference with beamsplitters. A circular pola is recommended on film cameras with videotaps and most modern Sony cameras such as the EX and XDCAM models.
True-Pol and Ultra-Pol: Brand names for high performance polarizers that have an increased polarizing effect that also block more light. These filters are available in Linear or Circular.
Water White and HD: Brand names for filters that use higher quality optical glass. Available along with the other options.
One-stop Pola: A weaker polarizing effect which only blocks one stop of light.
85 Pola or Warm Pola: Polarizing filters that are combined with other common filters such as an 85 color correction or an 812 warming filter.