CPL Filter - Pros & Cons

[Panzer Platform]

Hello, and welcome to my first official Dash Cam Talk forum post.
Let me start by saying I’m new to dash cams, and I’m basically a true amateur, and I’m hoping I can learn from all your expertise.

I would like to get your feedback on the Pros & Cons of using a CPL Filter on a dash cam to mitigate window glare. I’m a huge fan how they work wonderfully during the daytime to almost eliminate window glare. However, I’m less than enchanted with their use during night time, and low light driving conditions.

Based on my limited first hand experience, I found that leaving the CPL Filter on during night time driving, made my footage appear darker, and it had a slight yellowish tint. Of course, the simplest solution is to remove the CPL Filter for night driving, but that would fall somewhere between an inconvenience, and forgetting to remove it all together.

I’ve read customer feedback that said over time due to normal road vibration the CPL Filter can become misaligned, and cause even more degradation to the recorded footage. So it’s recommended to periodically check the alignment to make sure it has not rotated from it’s intended position. This sounds like one more maintenance check to keep up on, that I will most likely neglect until it’s too late.

So, I went looking for alternative solutions, and came upon a YouTube Video from “Phil UK Net”. He does an excellent job explaining how CPL Filters reduce available light to the camera lens / sensor, and offers a simple DIY alternative. I’ll leave a link to Phil’s video down below.

I also cam across a YouTube Video from “LifeHackster”. He demonstrates a product that essentially works like Phil’s DIY solution, but has a much better fit & finish, and aesthetic appearance. I wonder if dash cam manufacturers will ever make this accessory, it looks like it would work for my application. I’ll leave a link to LifeHackster’s video down below.

Next topic.
I’ve read a general rule of thumb is to adjust the dash cam so the horizon line is in the middle of recorded footage, (50% sky / 50% road). By accident one day I noticed my camera became misadjusted buy placing, and removing my windshield sunshade, and when I reviewed the recorded footage I had around 70% sky, and 30% road. I noticed immediately that my usually windshield glare was all but eliminated except for a very small proportion on the bottom corners of the footage. I kept watching the camera footage to see if cars, and their license plates were still in frame, and still readable. To my surprise they were, and most importantly I could still read license plates. So for the past few months I’ve been driving around with all my dash cams adjusted 70% sky 30% road thinking everything was hunky dory.

Well, I’ve now learned that this also creates another problem thanks to Dadi_T. He said aiming the camera to high will “produce dark videos and bad exposure”. I don’t have a full understanding how this works, but I think he’s saying the bright sun will cause the camera to automatically “dim” itself. Please forgive my laymen explanation.

If you made it this far, thanks for your time, and I’m looking forward to reading what you guys have to say about this topic.
Thanks again,
-Chuck

Phil UK Net;

LifeHackster;

 

[kamkar]

Since the CPL filters became the norm have i used them permanently.
It is a fact that they do block a little light, but as i just want my dashcam to log my own driving in regard to my speed - lane holding in relation to road side or lane markings, and document the color of the lights i pass thru, then i am good with any dashcams low light performance.

Dont get me wrong i do wish for much more, but i am ultra realistic about what i know i am going to get,,,,,,,, also why elections in Denmark are such a nightmare for me, or for that matter just the simple ( not simple to me ) thing of making friends.

As a matter of fact i even have a dash mat in my car too, so i dont really need a CPL filter, but as the CPL only take care of some reflections the mat take care of the rest. ( well aside for the cut out in the dash mat for my windscreen defroster vents )

If you have a windscreen that is polarized or the after market ting on it are, then that is bad, as dual CPL filters create distortion in the footage, often seen as a multi color rainbow effect.

The cameras aim have something to do with the light metering it use, and according to that select the ISO range to use, if the cameras was full blown the aperture could also be a played here, but that do not exist on the little lenses in dash or action cameras, so our cameras just have the ISO and exposure "knob" to adjust on.
Today cameras have a wider dynamic area and so the aim are not as important as it use to be 10 years ago where a 60/40 split was the norm, nowadays you just have to aim it strait and you should be good.

 

[Panzer Platform]

Since the CPL filters became the norm have i used them permanently.
It is a fact that they do block a little light, but as i just want my dashcam to log my own driving in regard to my speed - lane holding in relation to road side or lane markings, and document the color of the lights i pass thru, then i am good with any dashcams low light performance.

Dont get me wrong i do wish for much more, but i am ultra realistic about what i know i am going to get,,,,,,,, also why elections in Denmark are such a nightmare for me, or for that matter just the simple ( not simple to me ) thing of making friends.

As a matter of fact i even have a dash mat in my car too, so i dont really need a CPL filter, but as the CPL only take care of some reflections the mat take care of the rest. ( well aside for the cut out in the dash mat for my windscreen defroster vents )

If you have a windscreen that is polarized or the after market ting on it are, then that is bad, as dual CPL filters create distortion in the footage, often seen as a multi color rainbow effect.

The cameras aim have something to do with the light metering it use, and according to that select the ISO range to use, if the cameras was full blown the aperture could also be a played here, but that do not exist on the little lenses in dash or action cameras, so our cameras just have the ISO and exposure "knob" to adjust on.
Today cameras have a wider dynamic area and so the aim are not as important as it use to be 10 years ago where a 60/40 split was the norm, nowadays you just have to aim it strait and you should be good.

Right on Kamkar,
Thanks for stopping in.
I forgot about those carpeted dash board covers, that another good idea.
I did not know some cars have polorized window glass, that's good to know.
Thanks again,
-Chuck

 

[Kremmen]

I'm the same. I had a dashcam once that had no way of fitting a filter and it was atrocious facing the sun or having the sun hit the windscreen from the side.

Yes it must compromise night footage but I'm certainly not removing and refitting it.

 

[Panzer Platform]

I'm the same. I had a dashcam once that had no way of fitting a filter and it was atrocious facing the sun or having the sun hit the windscreen from the side.

Yes it must compromise night footage but I'm certainly not removing and refitting it.

Right on Kremmen,
Thanks for stopping in.
Maybe one day in the future we'll have dash cams that automatically slide a CPL Filter into place when conditions warrant it.
And then slide away when not needed.
That would be neat. lol
-Chuck

 

[Kremmen]

Just don't go out in the dark and leave it fitted

 

[Nigel]

So, I went looking for alternative solutions, and came upon a YouTube Video from “Phil UK Net”. He does an excellent job explaining how CPL Filters reduce available light to the camera lens / sensor, and offers a simple DIY alternative. I’ll leave a link to Phil’s video down below.

I also cam across a YouTube Video from “LifeHackster”. He demonstrates a product that essentially works like Phil’s DIY solution, but has a much better fit & finish, and aesthetic appearance. I wonder if dash cam manufacturers will ever make this accessory, it looks like it would work for my application. I’ll leave a link to LifeHackster’s video down below.

The LifeHackster one will not work, it does not have the required field of view, unless mounted on a vertical window, as it was in the video.

Phil's is a lot better, and if you are movie making then it may be a very good choice, however it also has the problem of insufficient field of view, resulting in the mounts being visible in the image in his first attempt, and in him having to point the lens skywards to avoid the mounts in his second attempt. If you want to have the front of your car in view then this also does not work, and you should have the front of your car in view because if your video is forensically examined, the front of your car proves the field of view of the lens, without it you could be using a zoom lens, which would dramatically affect the apparent distances, without it you have poor quality evidence.

All this is to overcome losing 1 stop of light, which on a decent dashcam will double the amount of motion blur. It is good to have less motion blur, but is only an advantage in low light conditions, and in darkness you will have plenty of motion blur anyway, so loss of light due to the CPL is only a disadvantage a small amount of the time, whereas reflections, in some cars are a problem all of the time, and not having the front of your car visible is a disadvantage all of the time.

Overall, it is better to use a CPL than to use any of the alternatives people have come up with. If your car isn't too bad for reflections then maybe remove the CPL in winter when problem levels of low light are more frequent.

Phil's explanation of image noise and ISO is incorrect for most dashcams, dashcams should always be using high ISO to minimise motion blur, there is no reason to turn it down unlike when he is using his DSLR.

 

[Panzer Platform]

The LifeHackster one will not work, it does not have the required field of view, unless mounted on a vertical window, as it was in the video.

Phil's is a lot better, and if you are movie making then it may be a very good choice, however it also has the problem of insufficient field of view, resulting in the mounts being visible in the image in his first attempt, and in him having to point the lens skywards to avoid the mounts in his second attempt. If you want to have the front of your car in view then this also does not work, and you should have the front of your car in view because if your video is forensically examined, the front of your car proves the field of view of the lens, without it you could be using a zoom lens, which would dramatically affect the apparent distances, without it you have poor quality evidence.

All this is to overcome losing 1 stop of light, which on a decent dashcam will double the amount of motion blur. It is good to have less motion blur, but is only an advantage in low light conditions, and in darkness you will have plenty of motion blur anyway, so loss of light due to the CPL is only a disadvantage a small amount of the time, whereas reflections, in some cars are a problem all of the time, and not having the front of your car visible is a disadvantage all of the time.

Overall, it is better to use a CPL than to use any of the alternatives people have come up with. If your car isn't too bad for reflections then maybe remove the CPL in winter when problem levels of low light are more frequent.

Phil's explanation of image noise and ISO is incorrect for most dashcams, dashcams should always be using high ISO to minimise motion blur, there is no reason to turn it down unlike when he is using his DSLR.

Right on Nigel,
Thanks for stopping in.
Wow, this is a ton of information I did not know.
Thank you very much for the excellent reedback.
-Chuck

 

[Dashmellow]

I forgot about those carpeted dash board covers, that another good idea.

A dashmat is an excellent alternative to a CPL filter. In fact, a good dashmat can exceed the performance of a CPL, thus avoiding the exposure penalty inherent in the use of one.

Carpeted dash mats are a poor choice though as they are textured and usually made with shiny synthetic fibers that create their own reflection problems. A better choice is a smooth and flat matte finish "brushed suede" type that offers far better performance and a much nicer appearance.

You can see a good example of how well a dashmat alone can perform HERE, along with some explanatory discussion.

 

[Panzer Platform]

A dashmat is an excellent alternative to a CPL filter. In fact, a good dashmat can exceed the performance of a CPL, thus avoiding the exposure penalty inherent in the use of one.

Carpeted dash mats are a poor choice though as they are textured and usually made with shiny synthetic fibers that create their own reflection problems. A better choice is a smooth and flat matte finish "brushed suede" type that offers far better performance and a much nicer appearance.

You can see a good example of how well a dashmat alone can perform HERE, along with some explanatory discussion.

Right on Dashmellow,
Thank you for stopping in.
I read that whole posting you refered to.
That is great info I did not know.

I feel a little silly now, because my post is almost repetative.
But, before I posted I searched "CPL Filter" in the search bar at the top right corner, and couldn't find anything. lol
I looked for a way to delete this post, but I don't see one, only an edit feature.
Thanks again,
-Chuck