How to get rid of glare?

if I do the same with my polarised glasses the filter is at 90 degrees when it goes black, not at 45 degrees
 
is it supposed to be at a right angle (90 degrees)? According to
the CPL is supposed to be 45 degrees to go black.
 
I read a previous thread. Easiest way seems to be to hold the cpl filter to my eye looking out at the windshield. Rotate the CPL until I get the least amount of windshield reflection.
 
if I do the same with my polarised glasses the filter is at 90 degrees when it goes black, not at 45 degrees
It should always be black at 90 degrees to polarised driving glasses, that video is wrong!

Polarised driving glasses are doing exactly the same job as the CPL, removing horizontally polarized reflections, so they must be aligned the same, so clear at 0 degrees and black at 90.
 
It should always be black at 90 degrees to polarised driving glasses, that video is wrong!

Polarised driving glasses are doing exactly the same job as the CPL, removing horizontally polarized reflections, so they must be aligned the same, so clear at 0 degrees and black at 90.
I'm not sure how polarised glasses are normally done which is why I checked it against my own glasses, that would further suggest that his CPL filter is 45 degrees off from the correct setting, would easily explain why it has zero effect, I dare say it was adjusted correctly before he rotated the glass, not a fan of these how to videos that assume that anything you check it against is going to be aligned the same way as whatever they're using in the video, I'm sure the people that make these videos are well intentioned, just not well informed
 
I'm not sure that all polarized glasses are driving glasses, so maybe some are not perfectly vertically polarised, but driving glasses should be.

Checking it against the camera LCD is maybe a good way, most in car LCDs will be polarised at 45 degrees so that you can read them while wearing polarised driving glasses, but I'm not sure all camera screens are at 45 degrees, and even within a single model the screens sometimes get upgraded from one batch to another, plus some LCDs can be circularly polarised or not polarised at all, as in that Samsung phone.
 
Checking it against the camera LCD is maybe a good way
if they always have used the same LCD panels, hard to know if that's the case, in the video above it works, checked the CPL on the LCD on one of our cameras (DCPRO) and it doesn't black out regardless of the orientation of the filter, obviously a different type of panel
 
It would be nice if the piece of white paper actually worked, but even that seems remarkably easy to get sufficiently wrong that the CPL is not effective! Having them fixed at the factory and non-adjustable must be the best option.
 
It would be nice if the piece of white paper actually worked, but even that seems remarkably easy to get sufficiently wrong that the CPL is not effective! Having them fixed at the factory and non-adjustable must be the best option.
if you're eyeballing if you're off by 45 degrees or not it's good enough for that purpose, the filters only effective within a very small range
 
Amazing how the same subject keeps repeating itself along with the same arguments.

Going back nearly 5 years this exact discussion was had and the conclusion (at least mine) was that using any LCD panel to test the orientation of a CPL was pointless because there's no way to conclusively determine the orientation of a given panel. My own research with different panels I own (TVs, monitors, tablets, phones, etc.) showed 3 different orientations of the polarizing layer.

The method I used then, and still do because I've found no better/easier/accurate way, is using a printed test grid made up of different grey scale squares. Place it on the dash of the vehicle and rotate the CPL until the most squares are eliminated from the reflection in the windshield (windscreen) - the CPL is now oriented properly. I've tested this with multiple different lighting conditions and it works.

 
It is always best to test anything and everything as it is actually going to be used ;) Which in this case means mount the cam and the CPL and use the contrasting paper/scale-whatever on the dash to adjust the CPL to it's best position. Unless you're using your cam to record that LED display that is :whistle:

Phil
 
For those who want a deep dive into polarized light: https://en.wikipedia.org/wiki/Polarization_(waves)

Light that reflects off glass or water is polarized one way. Polarized sun glasses are polarized so that they block light that is reflected off a pool of water at a shallow angle. Since most windshields are at an angle what will generate the same polarization as a pool of water (cars all facing the same direction) polarized sun glasses will also reduce the reflections from windshields.
In this specific case, the wind shield is curved. so only one part of the windshield can have its glare reflections reduced. If you change the rotation of the CFL lens, the place on the windscreen where the reflection is reduced will move to a different location.
Most will want the CFL so that windscreen reflections from other cars are reduced, so they want the polarization the same as that of polarized sun glasses. This will result in the light being blocked completely when light first passes through the sun glasses and then through the CFL held at 90 degrees to the way it is mounted on the camera.

Why CFL (circularly polarized lens)? All of the above is a discussion of linear polarized light. Some cameras have a problem with polarized light. A CFL is a linear polarizer with a quarter wave plate. The quarter wave plate is made of a material that has a different index of refraction for different polarizations of light. The thickness of the quarter wave plate is such that it delays one polarization 1/4 of the wavelength of light. This is mounted such that the axis of the quarter wave plates polarization dependant index of refraction difference is at 45 degrees to the linear polarizer. This means that half of the polarized light is delayed by 90 degrees in phase, and you get a rotating electromagnetic wave. The cameras that are sensitive to polarized light don't see rotationaly polarized light as being polarized, so they are happy. The CFL still works to block light of a particular polarization when that light comes through the linear polarizer first.

Do not trust an LCD screen as a source for polarized light unless you know for certain that it is not a passive 3D TV screen. Passive 3D TV screens use rotational polarizers to alternately polarize rows of pixels either clockwise or counter clockwise. This allows the circular polarizers in 3D glasses to only allow the correct image to be seen by the correct eye. If you look at the screen through a linear polarizer, both images will get through, and rotating the linear polarizer would have no effect.
 
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