Circular Polarizers seem so confuse a lot of photographers! It’s a straightforward device (with complex science), but the polarizer causes people a lot of frustration because they don’t know how or when to use a polarizer. If you don’t feel like reading here is the “Cliff Notes” version; The only time to use a CPL (Circular Polarizing Filter) is when water is in the scene.
I know a lot of people do like the look of a CPL on blue skies, I don’t. For my taste, the CPL over-saturates skies, and they look fake and over-processed. There are ways to more realistically “fix” a dreary blue sky in Lightroom, but that’s a different blog post.
What is a Circular Polarizer used for?
A CPL will reduce or eliminate the glare, aka icky shiny spots on glass, water, or any wet things. See, that is pretty simple!
If you have had one of my image critiques, then you know I loathe anything that draws my eye away from the subject of the image. Imagine how I feel about hundreds of shiny things scattered through the image.
Supplied by Wikipedia
A polarizer or polariser is an optical filter that lets light waves of a specific polarization pass through while blocking light waves of other polarizations. It can filter a beam of light of undefined or mixed polarization into a beam of well-defined polarization, that is polarized light.
There are several ways to create circularly polarized light, the cheapest and most common involves placing a quarter-wave plate after a linear polarizer and directing unpolarized light through the linear polarizer. The linearly polarized light leaving the linear polarizer is transformed into circularly polarized light by the quarter wave plate. The transmission axis of the linear polarizer needs to be half way (45°) between the fast and slow axes of the quarter-wave plate.
When one attempts to pass unpolarized light through the linear polarizer, only light that has its electric field at the positive 45° angle leaves the linear polarizer and enters the quarter-wave plate. In the illustration, the three wavelengths of unpolarized light represented would be transformed into the three wavelengths of linearly polarized light on the other side of the linear polarizer.
Extra brownie points if that made sense!
How Do You Use a Circular Polarizer?
Attach the filter to the lens, and you rotate the ring on the front edge of the CPL to “polarize” the scene. The effect will vary by how much you turn the filter ring.
Look through the CPL in your hand and see what the filter will do to enhance the image. The light conditions may not always be right for a CPL.
CPL Before and After Images