There are two types of polarizing filters: Circular and Linear. Polarizing filters have several benefits and many photographers consider them an essential accessory. They are especailly useful for landscape photographers or anyone who likes to take photos outside and wants to reduce unwanted glare.
When purchasing a polarizing filter, choose carefully.
With polarizing filters, you get what you pay for
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.
Stay away from cheap polarizers as image quality will be strongly degraded. In fact, sometimes you can see the mesh on your pictures.
When buying a polarizing filter, get highest quality of glass you can afford for best picture quality and make sure it’s coated.
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 have more than one lens that have different sized filter-mounts, you may have to buy more than one filter.
If you don’t intend to use a DSLR, save money and buy a Linear polarizer.
If you use a wide angle lens, get a “slim” polarizing filter. It is thinner than a standard polarizer and should prevent vignetting.