A question we often get is: "Should I purchase a linear polarizer or a circular polarizer?, what's the difference?"
The short answer is that both Linear and Circular Polarizers do the same thing. The actual polarization effects such as reducing reflections on glass surfaces, increasing color saturation in foliage, darkening a blue sky are the same with both Linear and Circular polarizers.
Circular Polarizers contains a Linear Polarizer component that does the main work of polarization, as well as a second layer inside the filter called a Quarter Wave Plate, which “spins” the light after it goes through the linear layer and before it enters the camera lens.
The main problem that the circular polarizer addresses is cross polarization on other reflective surfaces in your system such as mirrors and beam splitters. Reflective surfaces polarize light . . . which is why a polarizer can reduce or eliminate those reflections. If you have a mirror or other reflective surface inside your camera, a linear polarizer can cross polarize the reflected image and possibly black out the image.
The classic problem in 35mm film production was the video tap. Using a linear polarizer on a film camera with a video tap, could and often would cause the video feed to go dark.
In still photography, SLR cameras and DSLR cameras have a mirror, which a linear polarizer can cross polarize, causing the image to darken or go black.
With a circular pol, the quarter wave plate on the rear of the polarizer spins the light before it enters the camera lens so that it doesn't get cross polarized on any reflective surfaces in the system, such as the partial mirror in a video tap.
The linear polarizer element in a circular polarizer needs to be out front, pointed at the world, with the quarter wave plate on the rear side, the camera lens side. A circular polarizer doesn’t work if you get it in backwards. With a screw-in filter that’s no issue. With drop-in and rectangular filters for cine matte boxes, the filters are labeled with “this side out”.
f there are mirrors in your optical system, the circular pol solves any problems or potential problems.
If you have no mirrors or reflective surfaces in your system, such as a DSLR mirror or a beam splitter . . . then the Linear-Pol will not cause you any trouble and you can’t put it in the matte box backwards, which might save you some time and trouble.
Lindsey Optics offers both circular and linear polarizers in professional cine sizes in 4.5" Round Drop-In, 138mm Round Drop-In, and 4"x5.65", all with anti-reflection coating.
Our newest and most interesting product is the Brilliant² Rota Pol, a circular polarizer made to fit in 4"x5.65" cine matte boxes::