A homemade polarizer switcher!

I’d been talking with a friend about how to make a linear polarizer switcher that didn’t cost an arm and a leg. Normally, a polarizer switcher costs between $1,300 and $5,000. The $1,300 polarizer switchers only handle circular polarization, which is useless to me. The cheapest polarizer switcher that can handle linear polarization is around $5,000. And that’s too expensive.

The goal is to conduct my 3D for Kids events without having to set up two projectors. It’s the single biggest time sink when setting up a workshop. I spend about 45 minutes messing with the two projectors. Even when the result is the best that it can be, it’s never perfect. There’s always a bit of misalignment in one of the corners. Or there’s a hint of vertical misalignment. In an ideal world, I’d like to set up a projector, put a device in front of it, then BOOM — linear polarized 3D with perfect alignment. That’s what I was hoping to do with the StereoVision Flexaron but became occupied with other commitments before being able to follow that through.

I tried doing some research on how to build a homemade polarizer swticher but came up empty-handed. It seems that nobody has ever attempted to make one, or at least nobody has documented how to make a DIY polarizer switcher online…until now!

I’d remarked to my friend that, when the shutter glasses are turned off, they almost seem to act like linear polarized glasses. (I noticed that I could see reflections off of my hardwood floor with one eye but not the other when the shutter glasses glasses were turned off.) My friend doesn’t own any active 3D glasses, so my comment inadvertently gave him the key in figuring out how to hack them.

Long story short: active 3D shutter glasses — at least the kind I have — have a linear polarizer followed by a LCD followed by another linear polarizer. My friend’s idea was to peel the inner linear polarizer off of the glasses and…it worked!

He used a pen knife to lift the corner of the polarizer, then used tweezers to fully remove the polarizer from the LCD. There were still a few bits of adhesive left on the LCD (which he tried to clean up with isopropyl alcohol), but those bits aren’t noticeable when the glasses are put as close to the projector lens as they are for this project.

Polarizer 0

polarizer 1

Note that the polarizers on the front of the glasses are at a 45 degree angle from the angle that most linear polarized glasses are positioned. That’s why the glasses are being held by the microphone clip at a 45 degree angle. I used my DIY filter stand (Page 1 Page 2 Page 3) to hold the glasses.

Note that these are DLP-Link glasses and the optical sensor is facing toward the projector instead of toward the screen. It doesn’t seem to cause a problem — the glasses are able to pick up the proper sync without facing the screen. Obviously, you must charge and turn on the glasses for the polarizer switcher to work.

Polarizer 2

The key to making this work is to get the entire frame from the projector into the glasses. So far, I haven’t seen any problem with the glasses absorbing the heat. The metal stand absorbs a LOT of heat, but the plastic glasses seem to be at room temperature when I move them away from playing a video at full brightness. I’ve watched full-length movies and the glasses don’t heat up at all.

Polarizer 3

There’s no vertical misalignment whatsoever — it looks the same as projecting a movie with DLP-Link, except the viewer has to wear linear polarized glasses.

Polarizer 4.

So…a $40 pair of shutter glasses can be hacked to do pretty much the same thing as a $5,000 polarizer switcher. Sure, I wouldn’t recommend this method if you’re running a commercial theater or an amusement park attraction, but for home viewing and presentations…it looks like it’s going to work out just fine. The result on the screen looks better than two properly aligned projectors. Plus, there’s the added bonus of keeping the projectionist’s blood pressure low.

Now…who wants to buy my StereoVision Flexaron? :)

Update #1: See Ron Labbe’s successful homemade polarizer switcher  for more details on how to build this project!

Update #2: I made two additional polarizer switchers and made a 3D video of the process:

 

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14 Responses to A homemade polarizer switcher!

  1. voicu alin says:

    hello dear sir , i want to ask you something, it is possible to make a 3d polarized swicher for circular polarized glasses, like realD, with one of the 3d dlp glasses on the market.thanks in advance for all . Regards.Alin V.

    • Jeff Boller says:

      I believe you would need a wave retarder plate and a circular polarizer to do this. I haven’t tried it myself nor am I sure what the correct order would be. If someone else wants to chime in and offer suggestions, feel free to do so!

  2. Blip says:

    Does this work for non-DLP projectors, for example using RF or IR 3D glasses?

    • Jeff Boller says:

      Good question. Although I don’t have a non-DLP projector to confirm it, I would imagine it would work. The principle behind how active shutter glasses work is the same, no matter if they’re getting a signal from RF or IR. The two things I would be concerned with are, 1) Can the glasses withstand the heat from the projector, and 2) Can the glasses still communicate with the projector when they are that close to the projector? (I’d imagine RF can, but IR might be trickier, if the glasses aren’t pointing at the receiver.)

  3. B says:

    I removed the inside layer from my Samsung glasses (they look just like your glasses, with a glass layer surrounded by two plastic polarizers), and connected them up to my JVC projector. I tried every angle but don’t get any 3D effect . Nothing happens at all when at a 90 degree angle, I still get two bright left/right images on the screen, and at a 1 80 degree angle the screen image just becomes dark. With the other remaining lens, I see one clear image, the one intended for that eye. Am I doing something wrong?

    • Jeff Boller says:

      Some things to check…most of these should be obvious, but just in case:

      1) Were you trying this out while wearing linear polarized glasses? (Glasses with circular polarization, like the Real-D glasses from cinemas, will not work.)

      2) Were you projecting onto a silver-backed screen, intended for polarized projection? (Polarized projection will not work on regular walls or ordinary screens.)

      3) Were the active glasses turned on? (I assume they were, since you said that you could see the other eye projected through correctly.)

      4) While you were wearing linear polarized glasses and holding onto your active glasses in front of the projector, when you put the eye where you cut out the filter, did you try rotating the active glasses slowly? The glasses I’ve tried this out on worked at a 45 degree angle — I haven’t seen 90 or 180 degrees work. That’s not to say that 45 degrees is the only possibility, though.

      If it’s possible for you to send a paused signal where there’s, say, the word “LEFT” for the left eye and the word “RIGHT” for the right eye, you can keep one of your eyes shut while wearing the linear polarized glasses, slowly rotate the active glasses in front of the projector, and it should be easy to see where the cancellation happens and only one eye is projected.

      If you’ve done all of those things and it’s still not working, you may have accidentally cut the signal going to the active glasses eye that has the polarizer peeled off. I’ve done this; it happens. The insides of the active glasses I’ve torn apart are really fragile; it’s easy for things to go wrong and you’ll never know it just by looking at it. If this seems to be the case, you still have a second shot at making it work by peeling the polarizer off of the other eye. Just make sure you remember which one is the (likely) good eye when you put the glasses in front of the projector.

      Hope this helps!

  4. B says:

    Jeff,

    I changed my 3D glasses for a pair of linear polarized glasses, and following your suggestion also projected onto some 3D screen samples that I have…it seems to work now :-) I didn’t realize the screen was so important. My screen samples are small, so I’m not sure how the 3D effect is, but I can clearly see a different image in each eye now. My last issue is I can’t get the image to fit inside the lens, it only covers about 70% of the image. I’m projecting a 130″ image and would like to go much bigger. Do you have any suggestion how to deal with this?

    Thanks for the detailed response, and sharing an awesome hack!

    • Jeff Boller says:

      Glad to hear you got it working. Are you able to put the glasses almost flush up against the projector lens? You will need to be careful that the glasses don’t get too hot over time, though.

      • B says:

        Yes, the glasses are right up against the lens. If I zoom out, then the glasses can cover the lens, but then the projected image is too small at my available distance. Could I remove the remaining linear polarizer filter and then use a separate linear polarizer filter, and use the glasses only for their active shutter function? I could then angle the filter however I wanted, and rotate the glasses to horizontal position for maximum light area. Would this work in theory?

  5. Santander says:

    used projector?
    model????

    • Jeff Boller says:

      I used a Vivitek D500 projector, but the model shouldn’t matter as long as it can handle DLP-Link active 3D glasses.

  6. Mic says:

    This is really awesome and might be just what i was looking for. I have a couple of questions tho.

    Does this have any (huge) disadvantages compared to using 2 polarized projectors?
    Does this have any (huge) disadvantages compared to just using the active glasses instead of polarized glasses?

    Also a couple of more questions :):
    – Do you have a loss in the horizontal resolution because of the passive technology?

    Also, how close to watching a passive 3dtv is this?

    • Jeff Boller says:

      Two polarized projectors are worse, as it’s really difficult to line up both projectors so that they are keystoned exactly the same. Plus, unless you always run them at the same time, the two polarized projectors might have slightly different brightness levels. I can’t really think of any disadvantages to the polarizer switcher over using two polarized projectors. I’ll never project with two polarized projectors again if I can help it.

      I prefer using active glasses over polarized glasses, as they have better cancellation, there’s no need for a polarized screen, and it’s trivial to set up compared to this hacked active glasses method. However, passive glasses are really cheap in comparison to active glasses. So if you need to project to a lot of people — or if you need to project to people who may break the glasses (kids) or take the glasses home with them, polarized is the way to go.

      There is no loss in horizontal resolution with this method. It’s the exact same resolution as if you were watching with active 3D glasses.

      I can’t compare this method to watching a passive 3D TV. I don’t own a 3D TV, only a few 3D projectors.

      Hope this helps!

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