What is a Circular Polarizing Filter (CPL) and How to Use it

The use of lens filters can transform your photograph completely, as it allows you to go beyond the usual and explore something creative with your gear. Among multiple filters, a circular polarizing filter (CPL) is one such creative tool using which you can enhance the final photo that appears on your camera LCD screen.

A circular polarizing filter is a landscape photographer’s best camera accessory as it allows you to capture vividness and contrast in a photo. I have even used it to capture cityscapes and trust me it completely changes the image once you have it mounted on your camera lens. Having said that, let me take you through detailed uses of a CPL filter.

 CPL Filter Enhances the Sky Color

One of the major disappointments while shooting cityscapes is that the color in the sky is not registered in your camera as accurately as it appears to your eyes, right? Even if you are able to match the colors in your photo, you might still find the sky to be dull or hazy.

With the use of a Circular Polarizing filter (CPL) on your lens, you can enhance the colors in the sky as well as the elements in your frame. This is made possible as the CPL filter, when rotated at a particular angle minimizes the haze in the sky and enhances the color by reducing the polarization effect caused by sunlight.

As you can see in the image above, the dome was appearing off-white in color and the sky was appearing a bit too bright. After applying the Manfrotto CPL filter on my Canon 24-70 f/2.8 lens, I was able to correctly expose the dome, the sky had a good amount of contrast and the clouds were also clearly visible.

Here is another before and after CPL filter comparison, let me know in the comments section below which one do you like better.

A CPL Filter Cuts Reflections

While taking photos of glass buildings or landscapes with a water body in the frame, it can be really challenging to get rid of the reflections being caused by sunlight. You might have to change your composition or wait for the light to change in order to get a reflection-free image.

Using a CPL filter can allow you to minimize the mirror image being caused by in the reflective element in your frame. All you have to do is simply rotate the filter to the required angle.

Discussing the two images above, you can clearly see how mounting the CPL filter almost completely eliminates the reflection visible in the water body. Isn’t that magical?

Here is another example of how rotating the CPL filter to the desired angle can allow you to minimize the reflections in any water body in your frame.

How to get the maximum polarization effect?

As the science states, the maximum polarization effect takes place at an angle of 90 degrees from the sun that move in a circular band. This means that if the sun is at the top, you would get equally lit sky if you are shooting at an angle of 90 degrees from the sun.

To get the exact frame where you should be positioning your camera to get the maximum benefit of the CPL filter simply make an “L-shape” using your thumb and the index finger. Just point your thumb towards the sun, and your index finger will give you the angle where you would get evenly lit sky and get the maximum benefit of the CPL filter.

Otherwise, you may get unevenly lit sky in your photos which would be hard to correct later in the post-processing stage.

Things to consider while using a CPL Filter

1 – It cuts the light

As you mount the CPL filter on your camera lens, it cuts some amount of light which may vary from 1-2 stops. It means that if you were earlier shooting at 1/1000th, f/16 and ISO 100, after mounting the CPL filter the exposure would decrease by let’s say 2-stops. So in order to let in 2-stops of more light, you will either have to:

1. Slow down the shutter speed from 1/1000th to 1/250th, or
2. Open up the aperture from f/16 to f/8, or
3. Increase the ISO from 100 to 400

So whenever you plan to use a CPL filter, remember that there is going to be a loss of light and you might have to compensate a bit to get the correct exposure.

2 – Avoid using a wide-angle lens

Using a wide-angle lens can sometimes result in uneven sky color or color variation. The CPL filter is not at fault here, it is because wider focal length would cover more of the sky and as we discussed above the polarization effect is maximum at 90 degrees. Now a wide angle lens would cover more area of the sky, thus resulting in color variations.

To get the maximum benefit and the best result using a CPL filter, try and avoid using a lens wider than 24mm.

3 – Do not always use the maximum degree of polarization

What we usually tend to do is use everything at the maximum value and degree possible, like we do with an f/1.8 or f/1.4 lens, right? You should always rotate the CPL filter 360 degrees and check the level of contrast, saturation, and reflection it is boosting or reducing, and then only decide the degree at which you want to use the filter.

Sometimes using the CPL filter at maximum degree might result in color variation as well, especially while using it on a wide-angle lens.

Conclusion

If you want to learn more about polarizing filters and see examples here are some other dPS articles on the topic:

• When NOT to use a Polarizing Filter
• Circular Polarizers Versus Graduated Neutral Density Filters for Landscape Photography
• How to Make Funky Colorful Images of Ordinary Plastic Objects Using a Polarizing Filter
• Why You MUST Have a Polarizer
• The Ultimate Guide to Nature and Outdoor Photography

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