Reducing dashboard reflections with a CPL (Circular Polarizer Filter)

Hi !

Dashboard reflections are a big problem when we take pictures inside a car, especially with action cams (because of the very large FOV).
I ordered a 37mm circular polarized filter to mount on my Xiaomi Yi. Here is my first test (car stopped) :
Without CPL :

With CPL (set to max) :

It’s not perfect, but better.
The more the reflection is near the center, the more it’s efficient.

I’ve tested it on my smartphone, and it’s efficient too, but you need to find a way to mount it.

Now, I have to test it when the car moves as this filter reduce the light.

8 Likes

In addition to his @StephaneP

  • Remove lighter objects from the dashboard (place black blanket over dash if necessary)
  • Adjust the angle of the mount upwards so that the hood of the car is no longer shown
  • Keep the windshield clear of dirt and insects
1 Like

I’ve gotten to where I clean my windshield almost every time I stop for gas these days. Didn’t used to bother, even though the bugs bugged me.

Another possibility is to mount the camera up high–I have mine mounted in line with the rearview mirror, and that lets me point it straight ahead instead of having to angle it upward.

1 Like

Thanks @JackTheRipper. Good tips

You know how to spot Mapillarying cars ? The windshield is cleaner on the passenger side :smiley:

5 Likes

Does anyone have experience with polarizing filters for smartphones like this one?

Getting that camera lens right up next to the windshield will take care of 95% of the issue… or maybe 84% or 99.04%. You get the reflection because of the angles and the space between the surfaces.

Your filter doesn’t reduce the angles and the reflections, it’s just blocking light. You’ve noticed this as things are darker than they were before. Get that camera as close as possible.

I’ll try to remember to take a picture of mine to share.

1 Like

A polarizer reduces certain kinds of reflections, e.g. from water. I don’t know if reflections in glass counts too.

What I do know is, that they reduce the amount of light getting into the camera, so only use them when there is a lot of light. They also only works if rotated correctly. If you just set it at a random rotation, it will most likely only remove light in general.

I too joins the tips from @travel193 . If using an action cam, consider if it is safe to mount it outside.

Well, I remembered to snap a pic but this doesn’t show well how close the camera is the the windshield ( or windscreen or whatever name there is for it ). It minimizes the problem since it’s caused by the changes in surfaces the light’s bouncing off of. Ideally It’d up against the windshild with some sort of suction cup sleeve thing keeping it against the glass.

4 Likes

Great tip from @talllguy is to use black felt on the dashboard!

Thanks @katrin. Yes, the black felt works really well. I clean the inside and outside of the glass first with a window cleaner and microfiber cloth, then I lay a large piece of black felt on the dash. The felt prevents the reflection from my ugly gray dashboard from being reflected on the window.

Here’s the setup:

Here’s how the result looks on a bright sunny day.

8 Likes

Great idea, @tallguy

Great tip @talllguy. Adding this one to the wiki :wink:

Looks like @katrin already added it :smile:

There is a way to get a CPL for (nearly) free. All you need are 3D glasses from the cinema (usually disposable articles). If you are not passionated in watching movies (like me) you might have to ask a fried (my friends have “thousands” of them at home).

Detail note: Some cinemas are using other technologies than Polarized 3D system and won’t work therefore.

Follow these (trivial) steps to get your CPL:

  • Detach one of the lenses of the 3D glasses.
  • Place it in front of your (mobile phone) camera.
  • Aim a window (with a lot of reflections).
  • Rotate the lens (of the 3d glasses) in front of your camera until you get the best result (sometimes you get better results when you turn the lens round).
  • stick the lens with tape (or unicorn stickers :wink: )

This is what it looks like on my phone (I’m shure you can do it much better (e. g. cut out a part of the lens, use “real” tape):


This is what my dashbooard looks like:


And here a few shots for comapring (first image: without 3d glasses, second: with 3d glasses, photos where shot by mapillary app):


As mentioned in the wikipedia article the color of vegetation appears a bit different:


As you can see: Also the reflections of the window of the other car are reduced. :blush:

Imho the results are awesome (especially for a costless solution).

greetings
descilla

9 Likes

@descilla Wow! This is remarkable! How did you get the idea to try this? Adding it to the wiki :slight_smile:

Took me long enough but it’s on the wiki now. Thanks @descilla!

https://github.com/mapillary/UserGuide/wiki/Capturing#the-self-made-polarizing-filter

1 Like

I fixed my glare issues by getting a dashboard mat. It is cut and shaped to the dash of the car so it fits snug.

1 Like

just a recent example i noticed of how well some black fabric can stop reflections. the dashboard is showing at the bottom right… most of everything else on the left side of the image would have been hard to see if i didnt have the dash covered

1 Like

Hello everyone,
A polarizer reduces certain kinds of reflections, e.g. from water. I don’t know if reflections in glass counts too.

What I do know is, that they reduce the amount of light getting into the camera, so only use them when there is a lot of light. They also only works if rotated correctly. If you just set it at a random rotation, it will most likely only remove light in general.

I too joins the tips from @travel193 . If using an action cam, consider if it is safe to mount it outside.

1 Like