A while ago, I wrote a bit about how 3D movies work. One thing I said was
One experiment I wish I'd tried during te movie: put the glasses on upside down, so that the image meant for the left eye goes to the right eye and vice versa. This should have two effects:
- Make you look even goofier than the other people in the room wearing 3D glasses.
- Show you the picture inverted in depth (close stuff looks far and far stuff looks close).
If you try this during a 3D movie, let me know if it works (particularly #2 €” I'm pretty confident about #1).
As every theoretical physicist knows, there’s a danger in making predictions: someone will go out and do the experiment. My friend Tim Savage comments
Ted, we went to see the 3-D version of "Cloudy with a Chance of Meatballs" yesterday, so I tried your experiment of turning the glasses upside down. I'm sorry to report that you were wrong. It doesn't reverse the depth, it just flattens things out a bit. That is to say, the things that are supposed to be forward are still forward, just not as much so, although a little bit more than in a traditional 2-D picture. It does give you a headache if you try it several times, though.
A crushing blow.
Even stranger because I’ve subsequently read a bunch of things, including this article in The Physics Teacher, indicating that the model I described was more or less right. I’m at a loss to explain the data at the moment. I think I’ll have to go see another 3D movie to see if I can reproduce Tim’s result.
Any further experimental data or theoretical insight will be gladly welcomed.
I think you should carefully consider observer error.
That’s certainly the explanation most consistent with Eddington’s principle. (Never believe an experiment until it’s been confirmed by a theory.)
It’s worth bearing in mind that stereoscopic vision is only one of several cues used to perceive three-dimensionality, so it’s possible that even if I’m right about the physics my prediction was wrong as a matter of human perception.
I think I want to see Tim Burton’s Alice in Wonderland, so I’ll try the experiment myself then.
shouldn’t it work if you turn your glasses around backward, not flip them upside down? i thought the newfangled 3D glasses use 45-degree reflections that send the image towards the center of your eye. upside down lenses would possibly send the image out to your peripheral vision.
New experimental evidence:
Turning your glasses 180 degrees about the horizontal axis does invert the image, but because of the strength of other visual cues, it’s hardly noticeable unless you focus for a while on something in particular. The effect is more just to make things sort of fuzzy and flat–and also a bit confusing. Fast scenes (like the trailer for How To Train Your Dragon before Alice in Wonderland) are difficult for your brain to process–sorting out the cues becomes very confusing.