CPL Filter Positioning?

RavenManiac

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I just received a CPL filter for my A129. I didn't see an arrow indicating which side is up. Does it matter?

With my mini 0806, the filter could be adjusted by placing a piece of paper on the dashboard and then rotating the filter until the reflection of the paper is minimized. Can the Viofo filter be adjusted or is it fixed?
 
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RavenManiac

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Ok, good to know. Can the lens be rotated if it's not positioned correctly?
 
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I haven't checked it yet, but this video might be helpful to others who need to adjust their CPL filter.

 

Jeffmd

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My filter came rotated incorrectly by 90 degrees. I was baffled by the incompetence but thankfully holding the lens with a towel let me rotated it.
 
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My filter came rotated incorrectly by 90 degrees. I was baffled by the incompetence but thankfully holding the lens with a towel let me rotated it.
I need to check mine. There doesn't seem like that much glare reduction as it is. How's yours since you corrected it?
 

Jeffmd

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I need to check mine. There doesn't seem like that much glare reduction as it is. How's yours since you corrected it?
I just installed it, I could tell just by looking through it. So I hadn't used it in its incorrect state.
 

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Some times one cant but wonder how some people can mess up simple things.
We Danes have a saying for that.
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I was inspired by your video to check my CPL filters, 4 for 2 cars. And they all have a small red line on the side and the red line does correspond with the 45 degree angle that blacks out the screen! However, the 45 degree line does not correspond to the actual alignment to be honest.

I tried the way described in the video but when I aligned the filter so that it blacks/darkens out the screen of the dashcam at a 45 degree angle, I found it still reflected some parts of the dashboard. So what I did was, I pulled the round filter out of the housing and kept it in front of the lens of the camera, checking for reflections. Eventually I ended up with an almost 90 degree angle where there are no more reflections in the windscreen :O !

And then I put the filter back into the housing, where it does not reflect any part of the dash anymore, which is great!
 

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I also just installed the CPL filter for my A129 and was confused as to why there wasn't any change with it on or off. This was after rotating the lens so it turns black at a 45-degree angle. What I recommend is to sit in your vehicle and look at your windshield with the CPL lens. Rotate the lens of the CPL filter while looking through it with your own eye until there is the least amount of reflections in your windshield. Here are some screenshots comparing the before and after correcting the filter lens. I hope you find this helpful.Viofo A129 CPL Correct 2 (Ignition hand).jpgViofo A129 CPL Correct (Window hand).jpgViofo A129 CPL incorrect 2 (Ignition hand).jpgViofo A129 CPL incorrect (Window hand).jpg
 
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RavenManiac

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Another trick, which I picked up from Nigel, is to place a sheet of copy paper on the dash and rotate the CPL filter until the reflection is gone or nearly gone.

For those who have rotated their CPL filters, can you rotate it using the exposed edge of the filter at the top of the mount or do you need to sandwich it between your fingers?
 

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There is to much resistance and not enough surface area on the lip to grab from the edge, a soft cloth will do.
 

JPFrenette

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A polarizer filter need to be adjusted I'd say most of the time. The polarization of the light reflected will depend on the surface reflecting it so, a filter can't be mounted incorrectly at the factory, it's simply that in some case, what's from the factory won't do. RavenManiac's suggestion above is excellent
 

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A polarizer filter need to be adjusted I'd say most of the time. The polarization of the light reflected will depend on the surface reflecting it so, a filter can't be mounted incorrectly at the factory, it's simply that in some case, what's from the factory won't do. RavenManiac's suggestion above is excellent
Incorrect, the polarizer should always be aligned vertically so that it blocks horizontally polarized light, all the important reflections off the windscreen and road are horizontally polarised. The only correct factory alignment is vertical.
 

JPFrenette

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Nope, you're incorrect! ;) (I'm discussing, not trying to be an ass, I'm a newbie here! :) )


"...However, nonmetallic surfaces such as asphalt roadways, snowfields and water reflect light such that there is a large concentration of vibrations in a plane parallel to the reflecting surface. "

Don't forget the light isn't only polarized at "none", 0 or 90 degrees, it varies between horizontal and vertical. This is why polarizers for photo/video cameras are mounted so they can turn and the CPL for the A129 can turn.
If we're looking at a dashboard, it's not necessarily fully horizontal so the polarized reflection might not be 100% horizontal. Same as the windshield of a car behind/in front of you where reflections prevents you from seeing who's inside the car.

With a dashcam, most of the time the reflecting angle will be close to flat horizontal when we talk about the general view (the road) but the keyword is "most". If you want to lower the dash reflections, you might have to rotate the filter a bit, even if the "default" might work. One thing we don't know is, the "default" might be just random. We don't know if Viofo even pay attention to how it's shipped since it's quite possible it will need to be adjusted to see a difference between "meh" results and "Great", depending of the car and installation.
 

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Nope, you're incorrect! ;) (I'm discussing, not trying to be an ass, I'm a newbie here! :) )


"...However, nonmetallic surfaces such as asphalt roadways, snowfields and water reflect light such that there is a large concentration of vibrations in a plane parallel to the reflecting surface. "

Don't forget the light isn't only polarized at "none", 0 or 90 degrees, it varies between horizontal and vertical. This is why polarizers for photo/video cameras are mounted so they can turn and the CPL for the A129 can turn.
If we're looking at a dashboard, it's not necessarily fully horizontal so the polarized reflection might not be 100% horizontal. Same as the windshield of a car behind/in front of you where reflections prevents you from seeing who's inside the car.

With a dashcam, most of the time the reflecting angle will be close to flat horizontal when we talk about the general view (the road) but the keyword is "most". If you want to lower the dash reflections, you might have to rotate the filter a bit, even if the "default" might work. One thing we don't know is, the "default" might be just random. We don't know if Viofo even pay attention to how it's shipped since it's quite possible it will need to be adjusted to see a difference between "meh" results and "Great", depending of the car and installation.
:unsure: That is totally incorrect!
Except for the quote...

Since the camera should always be mounted parallel to the road surface, and the windscreen of your car and of cars in front and behind, vertical is always the correct alignment.

The angle of the dashboard does not matter, it is the angle of the surface reflecting the light that matters.

You would only need to adjust it if you were more interested in seeing through the windscreens of cars in the other lanes than in seeing through your own windscreen!

And yes, we do know that the manufacturer of Viofo's CPL filters carefully aligns them all so that they are vertical, or at least tries to, there have been a few threads where they got it wrong.

Have you ever seen polarised driving glasses that have rotatable lenses?
 
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