Circular Polarizing Lens (CPL) for Roav C1 Dashcam

Here is how I made a Circular Polarizing Filter for my Roav C1 Dashcam. This will help reduce glare coming off the windshield from sunlight during the day and headlights during the evening.

Step 1: Supplies Needed

The essential supplies needed to make this filter are all inexpensive and should be easy to obtain from a local hardware store and places like ebay. The Dremel is the only costly item but it isn't essential. Course sandpaper and hand sanding would work though the Dremel makes it much easier.

You will need:

1. One 7/8" "Drain" Stopper (under $2 at the local hardware store)
2. One pair of Polarizing 3D Movie Glasses (easily found on ebay for $1)
3. Cyanoacrylate Glue (Super Glue - $1)
4. X-acto knife
5. Dremel with Sanding Drum and Cutting Disc
6. Scissors

Step 2: Fitting the Drain Stopper to the Camera

The Roav C1 Dashcam lens housing is slightly larger then 7/8" which is why I chose the 7/8" drain stopper.

Take the drain stopper, and over/in a sink or something where fine dust won't be a problem, securely hold the drain stopper and start sanding the inside with the Dremel sanding drum to increase the size of the opening.
Try to sand the entire opening, not just the outer edge, and try to do it as evenly as possible all around the inside.

Every now and then, rinse off the dust from sanding, dry thoroughly, and test fit over the camera lens.
You want a slightly snug fit but one that will still allow you to rotate the stopper with a little effort.
Too tight and it will be hard to install and rotate but too loose and it will fall off.
Sand a little at a time and keep test fitting until you get a fit you're happy with.

Don't worry if the lens doesn't bottom out in the stopper, we'll check that later and will sand again to adjust.

Step 3: Cutting the Drain Stopper

Now that you have sanded the drain stopper to a fit you're happy with, it's time to cut an opening on the other side of the stopper.

Very Carefully take a sharp X-acto knife or equivalent and push it through the stopper from the inside out. Try and be near the inside wall as you go around but it's not critical to be up against it perfectly.

Pull the blade out, move it over slightly, and push it through again. Keep doing this until you have made all the cuts connected all the way around the stopper.
I found it was much easier to do it this way then to try and drag the blade around the stopper in one continuous motion.

Now pull out the center piece you have cut.

Step 4: Cleaning Up the New Opening

Now you are going to clean up the hole you made from cutting.

Carefully hold the drain stopper and use the Dremel sanding drum to sand the rough opening on a low speed setting.

Make sure to hold the drain stopper securely, but without squeezing as to distort its shape, because the Dremel has the possibility to grab and spin the stopper out of your fingers.

You want to sand the opening even all around and to be about the same size as the cameras outer lens housing.

Keep test fitting until you get it to the right size but when you do, you'll notice it doesn't fit down on the lens far enough. We'll take care of that in the next step.

Step 5: Cutting Down the Drain Stopper Height

To make the drain stopper fit far enough on to the camera lens you'll need to cut it down in size.
We want to be able to bottom out the cameras lens to the end of the drain stopper.

Hold the stopper next to the camera lens housing to get an idea of how much material you'll need to cut off the stopper. It's not a critical amount but you want to make sure to leave enough material so it will be able to stay securely mounted onto the cameras lens housing.

Take your Dremel with a cut off wheel attachment and cut the drain stopper down in size.
If your cut isn't even all around it won't matter as long as the drain stopper fits far enough down onto the camera. You can always sand your cut side flat later with the Dremel sanding drum or on a table with a piece of sandpaper.

After this, I colored the white stopper with a black felt marker so it would look better when the lens is put on it and when mounted on the camera.

Step 6: Preparing the Polarizing Lens

Take your polarizing 3D glasses and pull out one of the lenses.

Hold the lens in one hand, and while looking through it at your computer screen, start rotating the lens.
At some point you should see the screen become almost totally black. If not, flip the lens over to look through the other side and try again.

The side that you look through while rotating the lens that makes the screen turn black is also the side that the Camera Lens Must Look Through. This is the side you will glue the drain stopper to.

Take the lens and lay it down on a table or hard surface with the side you look through facing up. You may want to place something soft underneath it to protect the lens from getting scratched.

Take the Super Glue and put a small thin bead of it around the outside of the drain stopper face (the opening that doesn't push onto the camera) and then quickly place it onto the glasses lens.

Make sure when you place the drain stopper onto the lens that you don't slide it around. It must be placed down and not moved or else glue can get into the sight of the lens. Too much glue could also cause glue to leak into the lens sight area which is why a very small bead is all that is needed.

Wait until the glue is fully dried before moving on to the next step.

Step 7: Trimming the Lens

Once the glue has dried you can trim the lens with a scissor.

Cut all around as close as you can to the stopper.

Use the Dremel with the sanding drum to finish the edges that were too close to cut off with the scissor to get them smooth and flush with the stopper.

Step 8: Mount the Polarizing Filter

Once you have trimmed the lens, this is no longer a drain stopper but a Circular Polarizing Lens filter for a Roav C1 Dashcam!

Now you're ready to mount your new CPL to the camera.

Press it onto your camera and go mount the camera in the car so you can make the final position adjustment of the filter on the camera.

Step 9: Adjusting the Filter

With the camera mounted, turn it on so you can see the image on its lcd screen.

Place a piece of white paper on the dashboard close to the windshield.

This is where you will have to rotate the Polarizing Lens Filter on the camera.
If it is a little too hard to turn you can place it on the camera just slightly to make turning it easier.

While looking at the lcd screen of the camera, slowly rotate your new Polarizing Lens Filter until the maximum amount of the white paper disappears from view, this is the maximum filtering position of the lens.

Enjoy your new homemade Circular Polarizing Lens Filter (CPL)