Polarising filters give photographers more control over the lighting, reflections, and glare that their camera picks up. This is most noticeable when taking pictures of water. Rather than capturing images reflecting off the water, the photographer can take a photo of what lies underneath the water by cutting out the glare. Reputable companies like Cokin and Sigma all make camera filters. When buying polarising filters, keep in mind the camera type, mounting system, and look for helpful features.
Circular or Linear Polarising Filters
Only two kinds of polarising filters exist: circular and linear. Although different, they function the same, and the choice depends on the type of camera. For example, a circular polariser goes with models that have an auto-focus or spot-metering system. This usually includes most modern SLR cameras. Linear polarising filters conflict with the automated system, so they are typically for older generation film cameras. When shopping, remember that both filters are round, and their name has nothing to do with their shape. Sometimes, circular filters are abbreviated "CPL" or "PL-CIR", while linear ones are labelled "PL".
Circular or Square Filter Sets
The camera filter does not automatically fit onto the lens. Shoppers have to buy a filter set as well, which determines how the filter mounts onto the lens. With circular systems, users screw the filters into place. The disadvantage is that the mounting system only works with filters and lenses of one size. You may find 46 mm polarising filters on the lower end and 82 mm and larger on the upper end. Photographers who want to put on other filters have to buy step-down rings or a whole new mounting system. The filter holders mount onto the camera and have a slide-in mechanism. Putting the filter in is just a matter of sliding it into place. Switching back and forth between camera filters is much easier with this system, and adapters are available for those who want to change to another lens size. Photographers can also stack various filters on top of each other to create even more lighting effects. Unfortunately, the system adds bulky, which makes the camera more cumbersome to handle.
Polarising Filter Features
Some polarising filters have a few extra features to promote user-friendliness. For example, models with an index mark allow users to align the devices correctly. One with a screw-in arm can be much easier to rotate, especially for those who wear gloves. However, avoid polarising filters with thick rims because they can cause vignetting, which is the reduction of the photo's brightness around the edges of the image.