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Why I NEVER Use Circular Polarizing Filters (CPLs) With Drone Cameras

herein2021

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I thought we had a great discussion on ND filters and a lot of myths and misinformation was brought to light in my last food for thought thread where I discussed why I never use ND filters with drone cameras. One thing that came up a few times in that thread was using Circular Polarizing Lenses (CPLs) with drone cameras. So this week I thought I'd discuss why I never use CPLs with my drone cameras. Keep in mind this perspective is from a commercial photography/videography viewpoint, but the information could be useful to pretty much anyone considering using a CPL with their drone camera(s).

DEFINITION

A circular polarizer lens also known as a CPL for short is designed to remove reflections from the subject material. Reflections are typically caused when the sun hits a reflective object and the light from that object is captured by the lens. The end result of this is typically less appealing colors on bright sunny cloudless days, harsh reflections, and color loss due to reduced contrast.

HOW THEY WORK

Circular Polarizers consist of two pieces of glass (or plastic but hopefully glass) which are used to filter out light that has become polarized due to reflection from a non-metallic surface. In laymen's terms if light is reflecting off of certain surfaces it becomes polarized and the CPL can filter out the reflected light. CPL's, due to the filtering mechanism also tend to reduce the amount of light that hits the camera sensor by 1 or 2 stops.

There is one major catch to the way they work that for me eliminates them from being a viable solution for commercial drone photography or commercially viable video. A CPL needs its outer element to be rotated until it is 90 degrees in relation to the sun in order to filter out the polarized light. Even when filming from the ground, you do not typically use a CPL for sunrise or sunset footage because the sun is not at the proper angle in relation to the CPL.

DRONE USAGE

There are many CPL vendors for drone cameras including the EVO II series of drones. As I alluded to earlier, the problem with CPLs is that the front element must be rotated until it is 90 degrees in relation to the sun in order to get the full polarization effect.

The problem with this 90 degree requirement when it comes to drone cameras is that it is nearly impossible to predict what angle in relation to the sun the drone's camera will be when it is in the air and preparing to film a target subject.

This problem becomes much worse when filming video, as the drone rotates in relation to the sun and/or the camera tilts up or down, the strength of the CPL will fluctuate which could completely ruin an otherwise perfectly good take.

There is one possible scenario where the sun is at the proper angle, the CPL is properly rotated, and the drone takes off and flies in a straight line to the subject material without tilting the camera or turning the drone then flies straight back and lands. In this scenario the CPL could provide some benefit but in the real world this scenario is very limited and unlikely.

OTHER PROBLEMS

The problems with CPLs do not stop there. CPLs, just like ND filters, can introduce a whole host of other problems to your footage that would have been avoided if they were not used. Below is a list of some of those possible issues.

  • Color Cast - Just like with ND filters, CPL filters tend to introduce a green color cast to the footage you are filming with it. Of course this can be fixed in post....but it is an undesirable side effect that needs to be corrected in post (for commercially viable footage).
  • Uneven Gradient - Lower quality CPLs and CPLs that are not at the proper 90 degree angle to the sun can introduce an uneven gradient to the footage. This is pretty much impossible to remove from both images and video.
  • Lens Glare - Ironically, a CPL can actually introduce the very problem it was meant to solve by adding glare to the footage. This happens when the inner ring of the CPL is not coated black (many cheaper CPLs skip this step) and when the light reflects off of the inner ring of the CPL it creates glare which reduces contrast in the image.
The images below show some of these problems. These images were shot with a CPL attached to a Mavic Pro 2. I marked up the problem areas in the first image and let you see for yourself the problems in the second image. Not all CPL drone filters would introduce this level of image degradation, but it is a great illustration of how badly a CPL can impact otherwise quality footage.

Yacht Carrier 1.jpg Yacht Carrier 2.jpg

HOW TO GET THE BEST FOOTAGE WITHOUT A CPL

So now that you are aware of the damage a CPL can cause....I'm sure you must be asking; what do I do on those bright sunny cloudless days when the sun is reflecting off of the water/snow/shiny surface? Below is how I personally handle those situations:

  • Change the relationship between the drone and the sun - for this technique if the sun is causing harsh reflections I simply rotate the drone and/or tilt the drone's camera until I get a shot that has less glare in it. Obviously this does not always work so on to the next tip.
  • Shoot at a different time of day - If the sun at 11AM is creating a harsh glare off of the subject matter simply wait until 1PM......I can guarantee you that the glare will probably be gone. This is the most common technique that I use for commercial jobs. I simply pick a better time of day to shoot the footage. Commercial clients trust the person/people they hired to get them the best footage and are very understanding when I tell them what the best time of the day is for their shoot.
  • Fix it in post - If I can't move the drone, and I can't shoot at a different time of the day then I simply make the best of it while editing. For still photography you can use gradient filters to improve the sky and other washed out areas without affecting the rest of the image. For video work you can do the same thing by adding a gradient filter, key frames, and a tracking mask to reduce the glare and improve the colors.
  • What if I'm on vacation and just want good footage - Just get the drone in the air, properly expose the scene, and get what you can. The only one who would think you should have used a CPL is yourself....none of your audience who sees the footage later will know or care. For these scenarios you can also increase the contrast and up the saturation a bit while editing to counter the "washed out" look that the glare could have created.
CONCLUSION

Hopefully this post helps someone or some people get better footage from their drones. I personally have never even owned a drone CPL and I honestly rarely use CPLs even for my regular work. I mostly film people more so than landscapes or nature scenes and the last thing I want is to use a filter that could affect skin tones.

SPECIAL THANKS

I wish to thank @DsPallasVI for letting me use his images to demonstrate the problems a CPL can cause.

IN CASE YOU MISSED IT

Why I Never Use ND Filters With Drone Cameras

Autel EVO II Pro - User Experience from a DJI User

EXPLORE YOUR WORLD: An Autel EVO II Pro 6K Cinematic Story
 

herein2021

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Especially for this topic people are not interested in facts ;-)

But good explaination. CPL Filters for drones are nothing but snakeoil.

The whole camera industry is littered with snakeoil. I have drawers full of gadgets that seemed useful based on the marketing material at the time but were impractical in real life. Ironically my most useful tools are some of the simplest; camera cages, tripod plate adapters, camera handles, packing cases, multi-media card readers, etc.
 

Paulemus

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I don’t completely agree. Take, for example, polarized sunglasses. I always wear them while driving and looking around at different angles. There sure seems to be a lot less glare and harsh reflections off other cars with them than without them.
 
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herein2021

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I don’t completely agree. Take, for example, polarized sunglasses. I always wear them while driving and looking around at different angles. There sure seems to be a lot less glare and harsh reflections off other cars with them than without them.

Polarized sunglasses work differently from CPLs. Polarized sunglasses have a single lens vs a CPL which has two lenses, and polarized sunglasses use a chemical layer to polarize the horizontal light waves which blocks glare vs CPLs which use a quarter wave plate to remove polarized light.

Since polarized sunglasses have no way to rotate the polarization layer so that it is 90 degrees to the sun.....there is less control over the strength of the polarization. Sure they will cut down on glare at times, but it still depends on the relationship to the sun. Also, keep in mind that they are still sunglasses, by reducing the amount of light that reaches your eyes even if they are not actually blocking much via polarization filtering they are still reducing the light reaching your eyes which helps you see on bright days.

Polarized sunglasses just like CPLs need to be 90 degrees in relation to the sun in order to provide the strongest polarization benefits; as you turn and tilt your head at different angles the amount of polarization changes. But as I mentioned, they are still sunglasses, so to the human eye it can be difficult to tell what part is just reduction of light and what part is polarization. The varying levels of polarization aren't a big deal for sunglasses since its not video or photography so your eyes never know the difference. For video and photography, at least in the commercial world.....you need consistent predictable footage.

Also, with cameras you can't just let the CPL reduce the light by 1-2 stops and reduce the glare that way; if you did that the footage would certainly have less glare; but it would be 1-2 stops under exposed so you then have to adjust the exposure so that it is properly exposed. With sunglasses on the other hand, your eyes welcome the reduction in light and adjust for it so the glare is reduced by simple light reduction even before polarization is added.

As always, you don't have to take my word for it...a little research will say the same thing:

Myths About Polarized Glasses
 
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crusho

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Polarized sunglasses work differently from CPLs. Polarized sunglasses have a single lens vs a CPL which has two lenses, and polarized sunglasses use a chemical layer to polarize the horizontal light waves which blocks glare vs CPLs which use a quarter wave plate to remove polarized light.

Since polarized sunglasses have no way to rotate the polarization layer so that it is 90 degrees to the sun.....there is less control over the strength of the polarization. Sure they will cut down on glare at times, but it still depends on the relationship to the sun. Also, keep in mind that they are still sunglasses, by reducing the amount of light that reaches your eyes even if they are not actually blocking much via polarization filtering they are still reducing the light reaching your eyes which helps you see on bright days.

Polarized sunglasses just like CPLs need to be 90 degrees in relation to the sun in order to provide the strongest polarization benefits; as you turn and tilt your head at different angles the amount of polarization changes. But as I mentioned, they are still sunglasses, so to the human eye it can be difficult to tell what part is just reduction of light and what part is polarization. The varying levels of polarization aren't a big deal for sunglasses since its not video or photography so your eyes never know the difference. For video and photography, at least in the commercial world.....you need consistent predictable footage.

Also, with cameras you can't just let the CPL reduce the light by 1-2 stops and reduce the glare that way; if you did that the footage would certainly have less glare; but it would be 1-2 stops under exposed so you then have to adjust the exposure so that it is properly exposed. With sunglasses on the other hand, your eyes welcome the reduction in light and adjust for it so the glare is reduced by simple light reduction even before polarization is added.

As always, you don't have to take my word for it...a little research will say the same thing:

Myths About Polarized Glasses

Ang given that iPhone glass is polarized, it's always fun to have turn my head 90° while driving to see the screen on my mounted iPhone when when wearing polarized sunglasses. Otherwise? Black screen. At least I know the glasses' lenses are truly polarized ?.
 

herein2021

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Ang given that iPhone glass is polarized, it's always fun to have turn my head 90° while driving to see the screen on my mounted iPhone when when wearing polarized sunglasses. Otherwise? Black screen. At least I know the glasses' lenses are truly polarized ?.

Many LCD screens are impossible to see when wearing polarized sunglasses, I once pulled up to a gas station and forgot that I was wearing polarized sunglasses and thought the gas pump was broken because the displays were all blank. The iPad mini that I use with an anti-glare film seems to work fine with my polarized sunglasses; so it's really hit or miss with LCD screens.

According to the article below, if you were to rotate your iPhone by 90 degrees instead it would also fix the issue. I have an older iPhone (iPhone 6) and the screen is not polarized so I don't have that issue.

 

crusho

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Yea the tilting my head while driving was a bit of a joke; keeping it in horizontal mode in the mount solves the problem. But all this and the other thread (on ND filters in general) is making me realize how much extra drone money could have gone into my investment account. The Pandemic: Some people drank, some people baked, some people bought drones and mastered flying them, and some people bought a boatload of accessories before even mastering the basics. If someone told me ten years ago when I got my DSLR that I'd still spend most of my time in Auto 8 months later — without mastering shutter/aperture quirks for every lens I owned, I would have told them to get the heck out. Though I didn't have to pilot the Nikon. And video. And Autel took 3 months to repair my single crash, returning my E2 just in time for 20° temps and endless freezing rain. It was snowing yesterday.

Ok, I forgive myself.

Also, there are some places that are much more amenable to owning a drone (or three) than others.

Way off-topic here; my bad
 
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herein2021

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Yea the tilting my head while driving was a bit of a joke; keeping it in horizontal mode in the mount solves the problem. But all this and the other thread (on ND filters in general) is making me realize how much extra drone money could have gone into my investment account. The Pandemic: Some people drank, some people baked, some people bought drones and mastered flying them, and some people bought a boatload of accessories before even mastering the basics. If someone told me ten years ago when I got my DSLR that I'd still spend most of my time in Auto 8 months later — without mastering shutter/aperture quirks for every lens I owned, I would have told them to get the heck out. Though I didn't have to pilot the Nikon. And video. And Autel took 3 months to repair my single crash, returning my E2 just in time for 20° temps and endless freezing rain. It was snowing yesterday.

Ok, I forgive myself.

Also, there are some places that are much more amenable to owning a drone (or three) than others.

Way off-topic here; my bad

That's really my goal with threads like these, to help others see that there are two sides to every story. The most common story when it comes to cameras will be the one that sells products; not using or not buying something doesn't sell products so its not the side of the story that you will typically see on YouTube or websites. Nearly everyone has heard or read that you need to keep your shutter speed at 2x your framerate so of course you need an ND filter for that.....almost no one really analyzes how that rule came about and how applicable / or not applicable it is to drone footage.

CPL filters fall into this category as well...everyone wants better footage and that's what CPLs are advertised to provide. Its the details that make them a very poor choice for drone footage.

That's unfortunate about the crash, Autel is much smaller than DJI and especially with the pandemic, I can imagine customer service is even worse than usual; my current goal is to never need to use them.
 
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crusho

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I've never understood that rule either — like I said, I am new to video, but I like to shoot at 24 FPS, and I can think of a lot of reasons you wouldn't want to be "locked in" to 1/50 or 1/60th/sec.
 

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