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Little Tool—Big Results

by | Oct 22, 2021 | 0 comments

I have a simple tool in my camera bag that can be used to increase color saturation, reduce blowouts, cut through reflections and haze, and make blue skies richer. It is quite economical to own, yet so often overlooked when in the field photographing. It is a polarizing filter—a circular polarizer lens filter, to be exact, or a CPL for short. Circular polarizers can be rotated in a circle to work with differing light angles. A linear polarizer is set to one direction only, making it less useful many times.

The “secret” of a CPL lies in the science of how light works. Light is bouncing all around us, coming at us from all sides and angles. However, if the sun is reflected at the right angle, the light rays become polarized. These polarized rays overpower the light that would normally be reflected at us from objects in that direction. This creates a bright glare, like you might see on a body of water, or a really dark mirage, like you may see over asphalt.

A polarizer does its job by stopping the polarized light coming from one direction. With a circular polarizer, this direction can be changed by rotating the filter. If the glare is coming from a bright light source on the left side of the lens, for example, by turning the filter correctly, the light coming from the left will be diminished. This allows light coming from all other directions to enter normally. In this way, the glare from the left is reduced. If the photographer turns the camera so that the glare is now coming from the right, twisting the CPL light source indicator to the right will cause all light coming from the right side of the lens to be reduced.

Like all tools, there are cheaper models and higher quality ones. Cheaper filters are made from window glass and lack the multi-coatings of the better filters. The most expensive filters are made from optical glass, and have multi-resistant coatings (MRC). Just as glass and coatings affect the quality and price of lenses, so they also do on filters.
Having said this, I have not personally used the higher quality brands of CPL filters. So, even if you do not have the funds for a top-of-the-line filter, you can have fun results with a cheaper filter as I have.

Real results

Some of the results achieved by using a CPL are impossible to achieve in post-processing, even with the best software.

A common use of a CPL filter is to block glare on water surfaces. Fishermen know polarizer sunglasses help them see fish underwater. By the same token, a photograph of water taken with a polarizer will reveal underwater features such as rocks, that would otherwise be hidden by the glare.

© Mike Atnip

Glare on glass windows can also be reduced with a CPL, if seeing through them on a photo is important. There is a limit, of course, as to what to expect in these types of situations.

The same type of glare can be reduced on foliage. In addition to reducing glare, color saturation is improved. Remember this when photographing fall foliage shortly. You will probably find that the polarizer will give you naturally richer hues straight from the camera.

A CPL filter can also help when shooting in hazy or foggy conditions. Now it may be that you want the soft feel of a foggy morning. If so, leave off the CPL. But if you want to cut through the haze of a humid day, or perhaps even some smoggy cityscape, try the CPL. They have been known to reduce the flat look and make the colors pop through to a greater degree.

When we consider all the situations where unwanted reflections mess up our photos, the list can grow rather quickly. What about that shiny frog? The dew-bespeckled flower? The wet rock? Those moist eyes of that animal to which you were able to approach extremely close? It is no wonder that some photographers claim you should have a CPL on your camera at all times when outdoors.

When things go wrong

One of the things that drew my attention to CPL filters was that those blue October skies can be deeper and richer with a CPL. I love blue skies, and the perfect opportunity came one day when we were at Bethlehem, Pennsylvania, shooting some video for a historical documentary film on the missions of the Moravian Brethren. After shooting the historical locations downtown, we stopped by the remains of the old Bethlehem Steel factories. A century ago,
Bethlehem Steel was one of the largest steel factories in the world. Times have changed, and the old factories, acres and acres of them, were basically abandoned. Efforts have been made to clean up the area, letting the old steelworks stand as a monument.

There we were. Bright blue October skies. Rusty orange steelworks jutting hundreds of feet into the air in all sorts of interesting formations. The orange against the blue was a perfect match, and I took a lot of footage and still shots. I was feeling pretty good about my CPL. The photos appeared very attractive on the camera LCD, and I was excited about the potential.

You can imagine my letdown when I opened the pictures on my computer and found them to be terribly underexposed, grainy, and almost totally worthless! What went wrong?

The short story is that using CPL filters has a bit of a learning curve. For me that day, I think (but am not sure) that the problem was putting the CPL in front of a UV filter. I have since learned that digital camera sensors are already designed to deal with UV light and that a UV filter is unnecessary on digital cameras. Anyway, it seems that having both filters on together made the light splatter all over the place, into one big blotchy mess. It is possible, too, that a higher quality CPL would have made some difference. Never having used one, I can’t say how much of a difference that may have made. The whole experience was one of my biggest letdowns in photography.

Some drawbacks

1. CPL filters cut down on the amount of light entering the lens, so you will need a stop or two more on your exposure.

2. CPL filters produce uneven effects on wide-angle lenses, with a sky background. Go ahead and try one on that waterfall (to see through the water) if there is not much sky, but make sure you get some shots without the CPL in case things go funny.

3. They will not work on panoramas or stitched photos, since the angle of the glare changes as you sweep the camera.

4. From my own experience—and it may just be me—it seems that the LCD display of digital cameras does not always accurately display what the effect of the CPL will be. Until you understand how the CPL will affect a photo, it is advisable to take some shots without it so you do not lose your present opportunity, like I did at Bethlehem Steel.

Farm in Shenandoah Valley
The top photo was taken without a polarizer filter, the bottom with one. No post-processing was done.
Photos © Kevin Shank
Farm in Shenandoah Valley

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