Lens Filters: Circular Polarizer vs Polarizer
A polarizer lens filter is something that every serious photographer should own. It is fairly easy to mount a polarizer onto a camera. It screws directly over the lens. The purpose of a polarized filter is to filter out polarized light.
Polarization is light rays that are reflected off a non-metallic surface. Much of the light from the sky is polarized along with light that bounces off a large body of water or something else reflective like glass. The reason metallic light is not polarized lies in the electromagnetic nature of light itself.
A polarizer serves two purposes in photography:
The first is to darken the sky when you're shooting out doors. Shooting an exterior shot on a bright day can result in a light blue colored sky with the rest of the landscape slightly washed out. A polarizer filter will darken that sky making it a nice blue, while causing the rest of the landscapes to be nicely exposed and properly saturated in its color.This will also add more contrast to the image, improving its quality.
The second reason we use polarized filters is because it drastically reduces reflections. You would use the filter when shooting through glass or if you're shooting a landscape shot with a large body of water. Without the filter, the water would just look like a reflection of the environment around it. With the filter the water will look more like, water. This is also nice for shooting directly into water because you'll be able to see what's under the surface.
The transition from film to digital has not affected how we use polarized filters. Also, the effect from a polarized filter has to be done when the photograph is taken. You can not replicate its effects in photo editing software. Hence the reason why every photographer should own one.
Two Types of Polarization Filters
Generally, there are two types of polarization filters you can purchase: a Linear Polarizer and a Circular Polarizer. Both filters produce the same photographic effect, the only difference between the two is how they interact with your camera. Most new cameras are not compatible with a linear filter because of their auto-focus feature. That's because the beam splitters used to split the light for focusing are polarization-dependent.
How a Circular Polarizer Is Different
A circular polarizer is designed to compensate for this and works like a linear polarizer, except it allows some of the polarized through the lens for the camera to function properly. Circularized polarizers work with all cameras and are the ones that you should purchase for your camera.