Anti-glare filter made from 3D glasses (with pics & video)

[winterseed]

Hello good people! I signed up to share my experience so far with this little project.

The filter is just a piece of the lens from some disposable cinema 3D glasses. The first video has some examples with and without the filter on a sunny morning after rain the night before. Keep in mind that most of this is shot in deliberately awful conditions and my windscreen has 20+ years of wear & tear. Also, my camera (Kodak PlayTouch) has abysmal dynamic range and is a bit dumb with exposure sometimes. Enjoy:

The next video shows how I attach the filter to my cam and has a bunch of early morning test footage from a few days ago when it was overcast:

And some unedited comparison pics pulled from the video (filter on top, no filter on the bottom):

I'm pretty happy with it apart from the rainbow streaks which I guess are the result of imperfections in the filter. Apologies if my formatting/embedding results in tragedy. I tried.

 

[krellmk]

Nice

 

[Dashmellow]

If you search DashCamTalk for polarizer you'll find that this has been discussed many times already in numerous threads. I've tried it too, both with a DIY 3D movie glasses filter and with a commercial CPL filter. It works! There were two problems I encountered though. In a moving motor vehicle, the oblique angles of light are constantly changing, so therefore the angle of polarization keeps changing; sometimes the polarizer is quite effective and other times not so much. The other problem I ran into which I found much more vexing was that at night a polarizer is not a good idea if you want good dynamic range, exposure and image quality. It soon became obvious that the filter needs to be removed at night but for the life of me I kept forgetting to do that! I would review my night time footage and say, "Oh $%^&*!, I forgot to remove the F&%$^&*# filter again!" In the end, I gave up on polarizers. I realized that even with the glare and reflections, which are unpleasant, I still actually capture what I need to capture.

Using a polarizer on a dash cam is a personal decision and "your mileage may vary" as they say but this was my experience.

 

[winterseed]

You make a good point about forgetting to remove the filter at night. Human error should never be underestimated. I've forgotten to remove my lens cap or even press the record button multiple times each, any such potential oversight should really be mitigated as a high priority. You just know something exciting will happen the one time you forget to do x or y and you'll miss it.

As for needing to adjust the angle, I'm not sure that's true. Fine tuning can help if there's more glare on the right or left side, but the light path is always dash -> windscreen -> camera so I don't think adjustment is necessary no matter how acrobatic your driving. I could easily be wrong.

 

[Dashmellow]

What I am talking is that the angle of the sun as it shines on your windscreen is constantly changing, therefore, optimum polarization needs to keep changing to match the angle of reflection. The degree of polarization depends on the material and on the angle at which the light is reflected. It is really a complex physics concept. Think of a polarizer as a kind of hair comb. Only light coming through at the exact angle of the comb teeth will get filtered. If the photons of light enter the comb teeth at a different angle they won't get filtered. That's why a polarizer needs to be turned (adjusted) to the angle of light hitting it to be effective. When you go to a 3D movie and wear the 3D glasses, the light is always coming from one direction, the screen. When you put the same polarizer lens on a dash cam, the light is constantly coming from different directions. See the Wikipedia article about polarization to gain a better understanding of this concept.

 

[winterseed]

Hmm... I might give up on trying to understand how it works and just determine IF it works for me and my needs. Observation so far had told me that the orientation doesn't need to be adjusted when I change heading (north, south, east, west) but maybe it will at different times of day? There's also a fair chance I wasn't observing closely enough and I'm already wrong. At any rate, I'll withhold further comment until I have some more data. Thanks for trying to help me understand

 

[Dashmellow]

Like I said, it works and it's a "personal decision" whether to use a polarizer and "your mileage may vary". It can certainly be worth doing but I decided it just wasn't for me. There's no reason to be defensive about using it if you like using it. Mostly, I got tired of forgetting to remove it at night.

 

[ServMe]

This thread has given me some valuable insights before I go attempting to attach a CPL filter to my mini0803 when it arrives. Based on the pictures posted, I couldn't spot too much of a difference between the comparison stills, and while reading the DIY CPL filter thread, it became clear that attaching a filter to your dashcam is not always so straightforward.

Changing the filter direction depending on the light angle hitting the windscreen and cam lens is practically impossible, and if one needs to remove it for night trips, I'm sure I'll forget about more often than not.

I think I'll skip adding any filter for the time being, maybe some day a manufacturer will include a filer by default in the future.

 

[extraoneya]

As I posted sometime ago..the whole idea of using a polarizing filter for a dashcam seems weird to this ol' 35mm camera guy. As Dashmellow pointed out, u have to turn the filter each time the position of the light changes...which is kinda hard to do in a car, PLUS u have to look through the camera lens to see what effect it's producing.

I got a polarizing filter with my FineVu Pros & routinely forgot to take it off at night...ALSO...because of the lousy attachment Finevu had for it, it's now in the bottom of my heater vent system because it came off the cam & rolled into the dash's top vent hole...

Trying to retrieve it in a 1966 Corvette by dismantling the dash is a major 2 day operation...which I'll leave for whoever gets the car after I'm dead?!*!%!

........unless of course, I die in the vette & the filter rolls out on it's own from the now permanently dissembled dash.....I can see it now......Mike the Paramedic asks, "Hey Joe, what's this round lens thing that is next to this poor guys smashed head?" "Oh wow, that's a polarizing lens filter for dashcams, just like the one I lost down my dash last year....give it to me, the guy doesn't need it anymore.

 

[Sunny]

If you search DashCamTalk for polarizer you'll find that this has been discussed many times already in numerous threads. I've tried it too, both with a DIY 3D movie glasses filter and with a commercial CPL filter. It works! There were two problems I encountered though. In a moving motor vehicle, the oblique angles of light are constantly changing, so therefore the angle of polarization keeps changing; sometimes the polarizer is quite effective and other times not so much. The other problem I ran into which I found much more vexing was that at night a polarizer is not a good idea if you want good dynamic range, exposure and image quality. It soon became obvious that the filter needs to be removed at night but for the life of me I kept forgetting to do that! I would review my night time footage and say, "Oh $%^&*!, I forgot to remove the F&%$^&*# filter again!" In the end, I gave up on polarizers. I realized that even with the glare and reflections, which are unpleasant, I still actually capture what I need to capture.

Using a polarizer on a dash cam is a personal decision and "your mileage may vary" as they say but this was my experience.

Do you really have to take the filter off at night?
Does it make videos really dark?

I see dash reflection even at night on the windshield.

 

[winterseed]

For me, the filter darkens the image too much at night. It might be okay in a bright city but with only regular street lighting and/or car headlights the filter does more harm than good. Reducing glare isn't worth the cost of overall light when the camera is already struggling.

 

[niko]

Even used at day time, CPL filter makes numberplate readings from moving cars slightly less compare to non-CPL.