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

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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.

What is a Circular Polarizing Filter and How to Use it

 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.

What is a Circular Polarizing Filter and How to Use it - blue sky before and after

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.

What is a Circular Polarizing Filter and How to Use it

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.

What is a Circular Polarizing Filter and How to Use it

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?

What is a Circular Polarizing Filter and How to Use it

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:

Read more from our Cameras & Equipment category

Kunal Malhotra is a photography enthusiast whose passion for photography started 6 years back during his college days. Kunal is also a photography blogger, based out of Delhi, India. He loves sharing his knowledge about photography with fellow aspiring photographers by writing regular posts on his blog. Some of his favorite genres of photography are product, street, fitness, and architecture.

  • Albin

    Good summary, I’d throw in that, unlike many other hardware filter types, there really is no way to replicate the effects of a CPL in post-processing software. Especially with water or glass surfaces, sometimes you want the reflection other times to see clearly through – you can’t adjust for that in Lightroom.

  • LFC4SB

    You mention that the filter should not be used at wider angle than 24mm & I’m assuming you mean on a full frame camera & not a crop sensor?

  • Arthur_P_Dent

    In the one picture, I think the reflection works better than the dirty-looking bottom of the pool.

  • Jean-Luc Coulon

    Hi,
    Thanks for the information.

    I would like to add some more details.
    1 – The angle of 90° “from the sum” can be very different when we are playing with the reflections as the light source can be anywhere…
    2 – The filter is very efficient on foliage. The foliage is often reflecting light an lacks saturation. The CPL has a strong effect in this case.
    3 – The same way, whe you are on the shore or in a woodland and there are wet stones, the CPL alows you to retreive the stones texture instead of a flat and bright surface.

    Regards

    Jean-Luc

  • Capiroto

    the point is not which photo is better, but the effect obtained.

  • pete guaron

    They are particularly useful when you’re trying to photograph a store window – they can cut reflections dramatically – the trick is that (instead of standing directly in front of the window) you stand slightly to one side, and use the polarising filter to reduce or eliminate the reflections.

  • Mike Wetjen

    You know, I can’t remember the last time I removed the CPL filters from most of my lenses. Is that a bad thing? It’s not like I have filters on /all/ of my lenses, but the majority…

  • These photos are just to demonstrate the result that you can get using a CPL filter, depending on the situation you are shooting in. We can always adjust the filter to capture desired result.

  • The only drawback could be that you are restricting the light to enter through the lens by around 1-2 stops. But if that is not a concern for you and you do not shoot much in low light conditions, then that shall be fine.

  • Yes exactly, I was talking about 24mm focal length on a full frame camera. It shall be around 36-38mm on a crop sensor.

  • Lee Gyamfi

    very informed

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  • TW Douglass

    I was shown how to use a CPL about 25 years ago. I keep one on my lens at all times. I think they’re great. Recently I was on a photo excursion and with my camera on a tripod and using live view I was able to show the group the effects of rotating the CPL. Several people said they were going to buy one the next day.

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