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.
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.
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.
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.
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: