One of the most useful accessories a photographer can own is a circular polarizer filter. It provides many benefits to the photog who regularly shoots landscape, nature or just about any type of outdoor images, and it’s effects really cannot be replicated in post-production. It’s been said by many, if you only own one filter, it should be a circular polarizer. I’d modify that to say, if you only own one filter aftera UV or 1A filter, it should be a circular polarizer.
(In all the examples in this post the left or top photo is without, the second is with the circular polarizer. All photos can be clicked on for a larger view.)
What is a circular polarizer and what does it do?
A CP filter actually is made of two pieces of glass. When installed on your lens, one is stationary and the other rotates. Working together, these two pieces of glass can have subtle to significant effects on your imagery. If you would like to know the scientific explanation of exactly how it works, I recommend this Wikipedia article, which is perfect for anyone who has a degree in quantum mechanics. Otherwise, what it comes down to is that a circular polarizer modifies the direction of light waves entering your lens the way a pair of polarized sunglasses effect your vision when you wear them on a bright sunny day.
Using a circular polarizer can result in:
Darkened skies:
Reduced reflections:
and Saturated colors:
And in a pinch, it will perform as a 1 to 2 stop neutral density filter.
The extent of the effects the filter will have on your images is a function of lighting conditions, the position of your subject with respect to the sun, and how you adjust the filter.
Why is it useful and how would I use a circular polarizer?
In low light or days when the sun is filtered by clouds, the filter will have no effect, other than to reduce the amount of light entering your lens. Typically, a circular polarizer will cost you 1 to 2 stops of light so under those conditions, you should remove the filter. But on bright, sunny days, a CP filter can be really effective.
I say “can be” because the sun needs to be shining on your subject at a 90 degree angle. There’s an easy way to determine if your subject is in the optimum position: hold your finger as if it were a gun (like a child would), and point it at your subject.
With your thumb standing up at a 90 degree angle while you’re finger is pointing at the subject, see if you can rotate your wrist and point your thumb at the sun. If you can, then the sun and your subject are at 90 degrees to one another. In this photo, my finger is pointing at the birch trees, and my thumb is pointing at the sun to my left, so the trees are in a good position. If the sun is approximately at 90 degrees, you can still get some effect from the filter, but if it’s way off, the effect will be little or none. Worst case, if the sun is behind you or your subject, there will be no effect from the filter.
The pointed finger also is helpful to determine what subjects are at the correct location with respect to the sun: point you finger at the sun, and then rotate your wrist, so that your upright thumb travels in a circle. Anything that your thumb points at will be at 90 degrees from the sun and will be able to benefit from the circular polarizer.
By rotating the front element of a circular polarizer, you can adjust the intensity of the effect it will have on your image. How much effect you dial in is largely a matter of artistic choice. If looks good to you, then it’s right. In the first photo I posted above, of the birch tree against the blue sky, I dialed in the maximum effect to demonstrate the darkened sky result. That’s a bit strong for my taste and I could have easily dialed it back a bit. Note too how in that picture, the circular polarizer increased the color of the foliage of the tree and brightened the white trunk.
Note too in the third image above, how the filter cut down the reflection on the foliage, allowing the green to be brighter and that red stem to really stand out.
In the above image, the filter darkened the sky and brought out the color of the lawn. It also brightened and defined the clouds.
Is there any downside to using a circular polarizer?
Absolutely yes. As previously stated, don’t use a CP when in a low light situation, such as a cloudy day, or when the sun is low or below the horizon, or in shade, and definitely not when you are indoors.
Do not use with a lens wider than about 28mm (in 35 mm terms). At that width, the sky will look uneven, with inconsistent coloring. When using my Nikon 18-200 lens, I’m cautious to not zoom out completely else I’ll get undesirable results.
Images shot for the purpose of making a panorama will also, when stitched together, provide uneven results in the sky.
I’ve also had difficulty when taking bracketed images for the purposes of tone-mapping into a single HDR image. The saturation of the colors, particularly the sky, multiplies when you merge the images, resulting in excessive, almost cartoonish colors.
Any other advice?
It’s seldom a good idea to stack filters unless you are using “thin” filters. A circular polarizer tends to be thicker due to the two pieces of glass, so I always remove any other filters before using a CP.
Lenses with rotating front elements will counter your CP’s filter rotation, so focus your lens first and then adjust your circular polarizer.
The cost of a circular polarizer varies based on the materials used in construction and the size, which of course has to fit your particular lens. They can range from as low as $30 to well over $1,000. If you decide to purchase one, research your options at a reputable retailer and stick with the brand names. There are many reasonably priced CP filters that will fit the typical 52mm kit lens for under $100, and larger lenses for under $200.
While it’s not a magic bullet and won’t save every outdoor image, under the right conditions, a circular polarizer can very effective and produce dramatic results. Generally, when I’m shooting outdoors on a sunny day, my CP filter is on.
I hope you’ll try a circular polarizer filter and let us know what you think.
Thanks for visiting 2 Guys Phot0! Posted by Ed
2 Guys Photo 
Excellent article! You covered all the practical matters in a very accessible fashion. This would have saved me tons of research a few years ago when I was trying to figure out whether I needed one.
Excellent article. I particularly like that trick with the pointing finger and thumb. I have one of these but don’t use it often enough.
You mention that if you have a lens with rotating front elements you need to focus first. But how do you know if you have such a lens?
Hi Art. You’d see the front of lens rotate as you focus it. A CP filter can still be used, but you’d have to focus first, then adjust the filter, while keeping the focus (and the lens) in place. A little tricky but doable. Thanks for the comment Art. Ed
I tried a polarizing filter once. I didn’t get good results and am not sure why. Mostly I thought it caused my images to lack clarity or be too dark. I might need to try EV to overexpose per the camera meter but get the right result with the filter. It’s hard to do these filters with my S3 but doable.
Hi Maryann. The meter in your S3 should adjust for the 1-2 stops you lose with the CP filter without you needing to adjust the EV. If your results were too dark, you might try rotating the filter to reduce the polarizing effect. I’m not sure why your images were lacking clarity though, unless there was something wrong with the filter or the way it was attached to the S3. Thanks for the comments, Ed
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Excellent article. Now I know what it means when they say shoot at 90 degrees to the sun.
Thanks Oddy, glad you found it helpful. Ed