HOW A CIRCULAR POLARIZER WORKS
Posted by Benjamin Newton on
Top 5 Reasons to Own a Circular Polarizer
Controls reflections on glass, water, leaves, and sky.
Increases color saturation
Removes atmospheric haze
Provides 1-2 stops of Neutral Density for longer exposures
Key Features to look for
All polarizers are not created equal and poor quality glass, low quality polarizing films, and bad frames can affect sharpness, resolution, contrast and color. Polarizing glass is made by sandwiching the "polarizing film" between 2 pieces of glass then using special adhesives and manufacturing processes to make them into a single unit. If anything gets messed up during this process then you end up with a filter that will ruin a great image. Here are features to look for:
- Optical Glass is best but a lot of great polarizers are made from "Water White" and "Hoya Clear" glass. So look for those terms.
- Optical Thin Polarizing Film is a must and should be stated by the manufacturer. Low quality and low cost filters will avoid optical grade films to save money.
- Multi-coatings are great because they improve light transmission and reduce the chance for flare and ghosting. Most polarizers are not multi-coated because it is harder and more expensive to apply the coating correctly. Hoya's top selling polarizers are multi-coated but we do make a few that aren't MC to save money and reach a price point.
- Black Rimmed glass means the manufacture took extra care to paint a black rim on the outside edge of the glass. This ensures light does not bounce around and off the surface of the filter frame, which can cause more flare and ghosting.
- HRT vs Standard polarizing films. The polarization effect is the same from both types but a HRT (High Rate Transmission) film allows 2/3 to a full stop more light to pass through the filter than a standard film. This translates to faster more accurate AF and easier viewing when using an optical viewfinder.
How a Polarizer Works and When to use it
A circular polarizer is designed to do one thing: remove or control reflections from surfaces like water, glass, paint, leaves, sky, buildings, streets, and the list goes on. When light hits those surfaces they create glare that increases highlights, reduces color and detail. Almost every scene contains some kind of glare, and a circular polarizing filter will help you control that glare before it ever gets to your image.
A polarizer frame is made of two pieces attached together. One holds the glass and the other attaches to your lens. So, once the filter is secured to the lens, the front part of the filter will rotate freely. It is this rotation that will allow you control the polarization effect. By looking through your viewfinder or at your screen begin rotating the filter until you get the amount of reflection removal you need. Depending on the lighting conditions the effect may be dramatic or subtle so really pay attention to the details and the areas that are most important to you to control. Below are examples of common subject where a circular polarizer is used.