There are two types of polarizing filters: Circular and Linear.

There are many ways to fabricate a polarizing filter. Inexpensive filters will be made with a tiny mesh grid, while more expensive ones require optical coatings. When buying a polarizing filter, get highest quality of glass you can afford for best picture quality.

Stay away from cheap polarizers as image quality will be strongly degraded. In fact, sometimes you can see the mesh on your pictures.

Linear or Circular polarizer?

Both types of polarizers affect light in exactly the same way. A Circular polarizer is basically a Linear polarizer with an added optical component on the back.

Why the difference?

Cameras with phase focusing, such as Single Lens Reflex cameras and Digital Single Lens Reflex cameras , need light in two polarization orientations to focus. The added component of a Circular polarizer makes sure the camera gets just that.

If you don’t intend to use a DSLR, save money and buy a Linear polarizer.

Slim polarizer

If you use a wide angle lens, get a “slim” polarizing filter. It is thinner than a standard polarizer and should prevent vignetting.