Project: DIY Polarizing filter for the Xiaomi Yi (free!)

[Gimp Slave]

Hey.

So here's a very simple project you might like. Really simple. Like scrapbooking, but, you know, useful. It shouldn't take anyone more than half an hour and doesn't require any special tools*. You guys have been so helpful to me, I'm hoping at least one person finds this useful as well... it's not as ground-breaking as discovering pentaquarks with the Large Hadron collider or anything, but then you may find more use for it than pentaquarks, too.

Let me say up-front you can purchase small threaded and push-on filters; CPLs, UVs, lens caps, etc. for $5-35usd from various Chinese online shops. Most are (naturally) made for the GoPro but can be fitted with some slight surgery and sticky tape to any Yi... none of them are this small, and with their adapters, they stick WAY out off the lens, and cause serious vignetting, but they are proper glass filters with some durability. Many camera filter makers support 37mm, and popular drones like DJIs have filter sets (a Phantom III/IV is 38mm) So if you dislike DIY and reading this post makes you think you want one, g**gle to the rescue.

Polarizers are great for... polarizing light. For dashcam'ers, they're very handy for removing unwanted scattered reflections from shiny surfaces like chrome, car finishes and auto & architectural glass. It darkens the asphalt beautifully. It enhances contrast. It's also good at night, although it increases visible noise slightly (due to increasing exposure) but it calms down headlight flares dramatically.

If you don't know the pros/cons of polarizers, Sean T. McHugh's "Cambridge in Colour" website has a nice introductory article: http://www.cambridgeincolour.com/tutorials/polarizing-filters.htm

The best thing about this project? It's essentially free, and a great way to recoup some of that ripped-off feeling from spending $25+ on that last 3D summer blockbuster you went to see. The optical quality of these filters is surprisingly good; there is a *slight* degradation of the image quality, but most will not notice it, especially with the Yi. This method of filter mounting is both wide enough and close enough to the housing that it doe not cause noticeable vignetting.

The following instructions are complete overkill! There's no way such a simple project requires this many words. It's obvious what's going on from the photos. You will not need to read all this!! It's just here for a reference, in case you get stuck.

Have fun!
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A push-on DIY polarization filter for small lens barrel cameras

You will need:

● Disposable 3D polarized movie glasses
● A soft/flexible ~1" half-height bottle cap from bottled water
● A round template, in this case a U.S. quarter dollar
● cyanoacrylate adhesive, crazy or otherwise (or contact/rubber cement)
● An applicator for the adhesive, in this case a hair pin
● A hook/loop cable tie, 3" or longer
● A marker, magic or otherwise
● A ruler, scaled in millimeter
● A cutting device, in this case scissors.
--
*if you have an X-acto knife, and know how to use it safely, it's even faster and neater than scissors.


Notes:

(I) If you can only find a 'hard' plastic bottle cap, stop now. Please do not attempt, at least with scissors.

(II) The polarizer lens is not protected in any way. Handle accordingly. (eg. do not "clean" on your abrasive T-shirt.)

(III) You must use an applicator to apply the most minimal amount of cyanoacrylate. Like the drop from a pin point. It is well known that cyanoacrylate fumes will "fog" plastics, not to mention it will bond to your skin oils and make your fingerprints on the filter permanent! It's a great C.S.I. tool, but you'll want to avoid doing this here.

(IV) Polarizers reduce available light. In testing, one made from the Real3D lens absorbs 1⅓ - 2 ƒ-stops depending on orientation.

(V) Polarizers on wide angle lenses such as our Yi can vary the effect across the scene. Because the angle is so wide, reflected light can come from so many directions, and that's just the way it is. This cannot be changed, it's just physics. We are using a thin film polarizer and in this respect it's just as good as commercial filters, still, you might still notice it.


Directions:

1) Remove the cap and make it dry. Even stainless steel scissors do get rust spots. Open scissors and poke a hole in the cap with the top (pointy) blade, and cut off the center disc part of the cap. Due to the way the bottle cap is shaped, specifically the lip that seals to the top of the bottle, you can't easily remove that last mm... this is good. You need this remaining bit to hold the polarizer film. TRIVIA: Depending on if the scissors are for lefties or righties, the top or upper blade will be different, but the 'top' blade is always the one that's most pointed.

2) Again, depending on your handed-ness, use the top blade to cut around the cap's inner seal; you should not need much pressure, the cap is very soft, and the lip of this seal will work as a guide for the scissor blade. After this is completed, you need to take that lip, and push it to the outside, where you can cut it off. Again, it provides it's own cutting guide.

3) This next part requires a bit of dexterity; use very tip of the top blade to shave/scrape the threads inside the cap. You don't have to fully remove them, but remove most for a good fit. If you remove them unevenly, the filter will spin with a wobble - it's not optically important, it's more aesthetics. Yes I know, it's a bottle cap and broken 3D glasses - junk. But still.

4) Cut the cable tie; math says that 23.25mm diameter * π = 73mm circumference, but the lens barrel is slightly tapered. I had to cut a few to determine that ~76mm was the sweet spot. It's more like 75.75mm, but that level of accuracy is difficult. Trim the thickness of the tie, 4mm or so. Test-fit it in the cap, that it will go around the ring without having any overlap. A small gap is fine. (I'm guessing this ruler was made pre-internet, or Westcott has a sense of humor. AN4L. Anyone needing a millimeter rule might be thought of as... well.)

5) Carefully separate the frame halves from the 3D movie glasses and take one of the filters. Or just push out the lens, carefully. Use your round template to cut out a circle. From the edge, not the center. You may want to construct more DIY fun with the polarizer film. Inspect the filter for scratches or scuffs, and re-cut another circle as necessary.

6) Test-fit in the cap. Trim or re-cut another as necessary. It has to be right; you have one chance to put the lens in the cap once the cyanoacrylate is applied - if you shift it around, you'll streak the filter with glue and likely make it unusable. Once you are satisfied with the fit, determine what side is what. This is easy, just look out a window through it. Turn the filter. If the light changes, like from a blue/ yellow / gray tints and back to blue, this is reversed; whereas if your reflection in the window disappears and reappears, this is the right way. Another way to tell, look at any LCD. LCD displays have polarizers, so turning the filter should make the TV / tablet / phone screen disappear... a caveat being, many are bidirectionally polarized and will create rainbow patterns. (Birefringence.)

You should mark the polarizer, so that you know which side you want facing forward, and where the strongest effect is. Rotating it back and forth to find the "center point" of the strongest effect is easy enough. (the effect rotates every 45° turn, that is to say, if it's the strongest at 12 o'clock, it's weakest will be 3 & 9, with another strong at 6 o'clock.) Make a tiny mark on the very edge. When you glue it to the cap, mark the cap as well.

7) Now comes the tricky part. You need to glue the filter to the cap, and then the hook\loop strip to the cap. I have made a few now, I just glue the filter down with 3 tiny dots of glue in a triangle, and by tiny I mean as tiny as possible with a pin point, on the lip. Just to be safe, I constantly blew on it to keep the fumes from fogging the filter, although considering the minuscule droplets I used it was probably unnecessary. A slight downward pressure with the marker cap can help "clamp" the parts for 10 seconds or so, and inspect your work.

Carefully glue in the strip of cable tie - soft side (loop) outward toward lens, hard side (hook) toward the bottle cap. Place one dot of glue on the end, nearer the top away from the filter, and anchor it's position. Then, slowly work your way around, add a drop of glue, press into place, check placement, and continue around. I think I used 8 drops total. I admit this always takes me the most time, being careful not to get glue anywhere or scratch the filter when so close to being finished. Depending on your dexterity and how much of the threads you removed, this step can take 10 seconds or a frustratingly long time.

Make sure all glue is dry before putting on the camera, but! That's it. You are done. I can't believe you read all this. Almost 9000 words. Damn.


Directions for Use:

(kidding!)

 

[niko]

another good bottle cap life hack !

 

[Matt_V939]

I did a similar thing with below differences:
- i used a black colored bottle cap (no need to put a black tape to avoid reflections)
- i carved the hole in order to have it sticking around the lens (reversed from the one shown here)
- i used a dremel rotating sandpaper bit to trim to final diameter in order to achieve exact final mounting
- easier to glue the polarizing "lens" on the outside of the cap base (other side than shown here)

 

[Gimp Slave]

Reflections? It's literally 1/3mm above the lens; there's no reflection from a thin cap like this. I tested this with the same white dome I use for calculating vignetting correction, there was zero difference. If the sun angle was just precisely so, I guess it's possible it could cause a flare. You could always hit it with a sharpie I guess.

Well, with actual tools I've made some DIY ones that look nice, funky colors of whatever lids, some spray-painted ones (and let the tacky paint do the work of the adhesive, too) even stacked ones that act as a variable ND filter. But the idea here is that you don't need anything special, just scissors. If you have a dremel and sandpaper and cutting discs and drill bit attachments, you could be making ones out of real materials, not trash like bottlecaps! 🙂

Outside of cap = No. Moving the filter away from the lens is a bad idea. Very bad. Gluing it to the top of the cap, you can actually focus on the filter, not through the filter. These lenses try to have an incredibly deep hyperfocal range, from ~20mm to the horizon! The closer to the lens, the better that it will be transparent, and that it won't cause reflections nor flares in the video/photo. On top of that, (ha! wordplay pun) if there is reflections you mention that this black tape will need to block, then glued on top so the edge of the filter is exposed, it too will need tape/paint/a sharpie to avoid being a light path. Remember there's no antiglare coatings here, this is not a proper photographic filter. Your design may have worked for you but I don't suggest that to anyone reading this.

When I first started this, it was sitting in the passenger seat of a car, trying to shoot through some plate glass window and not just the reflection of the car. So went to it with some leftover polarized glasses from Finding Dory and some gaff tape. It worked, but everytime light angle changed? Constantly ripping off the tape to re-position the filter was getting frustrating, hence taking a water bottle off the floor and gutting the cap with a my trusty EDC. Project was born. (if you're into blades, my Ken Onion designed Kershaw Blur with a blade made from Crucible Industries S30V steel made quick work of that evil bottle cap, but check your local laws as it's an assisted opening knife; like Matt above lists himself in Taiwan, a country where even self-defense is frowned upon - you get jumped by 3 guys trying to rob you, but pull a knife and and proceed to defend yourself, YOU go to jail... and if one of them dies, you get charged with murder! God forbid you carry a firearm.)

@niko: the master of dashcam DIY! 🙂 love those press-on magnetic CPLs.

 

[Sunny]

Yes, but I don't like white cap. It's too noticeable plus looks DIY.
Need to either spray black before gluing filter or just start with black cap.
Black on black is very discrete and few imperfections won't get noticed.

 

[Gimp Slave]

That is the best reason, because you don't like it! But, again, in talking optical properties, it does not affect the performance. I understand some people are driven by aesthetics, whereas I am 100% function over form. And, sadly, I have not seen any colored bottle caps in the half-height, thin, flexible style that are easy to cut with scissors. Hey! "too noticeable"?! That sounds perv-y, are you using your Xiaomi in places you don't want people to see the camera?! Do you run a .ash file that turns the sounds off?! 😱

You might be able to paint it with flat black spray paint. Something meant for flexible plastics like Krylon Fusion. And, there does exist flat black paint pens, like this one from Testors, but it needs a regular 24h cure time, it's not a marker, just enamel paint in pen form. I tried a Sharpie Pro on one, but it was just as shiny as my Brownells gun scratch cover pen. Works great on blued firearms, not so much on a plastic bottle cap. Doesn't look flat either. (non-reflective flat, that is).

BTW on a silver camera, the semi-transparent clear looks complimentary! Most people don't have the black Xiaomi Yi, but the yellow/green or white ones. So it probably looks better clear-framed.

Notice the "notch" of missing filter material on the left (camera left, right for us) See? Don't care about aesthetics. There is no lens in that area, so the fact that part of the filter is cut off is not important. Performance is what matters. The black camera filter ring is sprayed with a heavy coat of Krylon (there are drips) It was made from a pill bottle cap, and definitely not cut out with scissors. But so far, it hasn't chipped or flaked. That is some polymer magic, Krylon!

Remember that the keys here are 1) easy to do without 'real' tools and 2) free. A $10 can of spray paint negates that, when you can buy a commercially made aluminum & glass CPL, already painted black, for $7usd from banggood or aliexpress.

 

[Sunny]

I'm not saying it's bad. I just don't like white colored cap on black camera whether it's DIY or commercial because it removes discreteness of the dashcam.
Besides that, personally I think $7 is much cheaper than spending an hour of my time.

However, it's good to have DIY option and thanks for your efforts as many find DIY a fun thing to do.
I do enjoy DIY but in different things.

 

[Matt_V939]

........ But the idea here is that you don't need anything special, just scissors. If you have a dremel and sandpaper and cutting discs and drill bit attachments, you could be making ones out of real materials, not trash like bottlecaps! 🙂

Outside of cap = No. Moving the filter away from the lens is a bad idea. Very bad. Gluing it to the top of the cap, you can actually focus on the filter, not through the filter. .....

Well:
1) with the dremel is easier to get the right diameter (and a round hole) than with scissor
2) "away from the lens": you can always CUT the excessive lenght of the cap (using it reversed as I wrote) and put the filter as close as you want.

 

[Gimp Slave]

The whole idea is it takes a half hour and you make it from (essentially) trash, for free and with tools that everyone is guaranteed to have, and it's more re-usable than just taping the film over your lens. In America, everyone with kids has some polarized 3D movie glasses somewhere, usually left in the car after the movie. Many people stupidly wear them as sunglasses, too. They are literally everywhere. Same for water bottles and scissors. A Dremel or other high speed rotary tool is a $50+ item that requires electricity, attachments, and some skill in using it to avoid injury. Scissors, everyone already has many years experience using them, since, what? 3rd grade / 8 yrs old? When you could move up from safety scissors to "real" ones?

FYI there are a bunch of DIY-polarizers-made-from-household-items articles all over the web, most are more elaborate than this. Some are damn impressive and I think the creators get too caught up in it, which hey, does happen. It's hard to remind yourself that at a certain point, even if you bought one of the industry standard "pro" polarizers like a ~$100usd B+W Circular Polarizer MRC Filter you'd still come out ahead as far as hours spent.

BTW, when compared to holding up a real polarizing filter in front of the Xiaomi vs this DIY one? It's damn good! Especially considering the price is nothing. Thanks Real3D!

 

[Matt_V939]

....In America, everyone with kids has some polarized 3D movie glasses somewhere, ..... A Dremel or other high speed rotary tool is a $50+ item that requires electricity, attachments, and some skill in using it to avoid injury.....
View attachment 25931

Well, I hope in America you have electricity as well....😉
You can also get these cheap rotary thing, this came even w/o a power supply (i use 12V Hard disk), I think I paid like 10$ (might be even less)

 

[Gimp Slave]

What's all that plastic stuff? is this the cutter from your CNC machine or something? I so want one. If I ever win the lottery I'd probably buy one of these. Just for fun.

Also dude. Please reduce the size of your image. That's excessive even if it were showing some procedure, but a static product shot? 1920x1440? Remember, most people are viewing on cell phones. Don't be inconsiderate. Mine are 480x320.

I do not think you are stupid, but you keep pushing tools tools tools... so that means you think I am stupid! lol. YES of course it could be improved; the whole idea is to not require real tools. So I must give up trying to explain. :-(

With tools and paint you can make a very professional polarizing filter... but that is not this project.

(Although if you do make one for the Yi, post it, and do a linkback here so people can see a nicer one to make.)