Bolt, RealD and circular polarization

Yesterday I watched Bolt in RealD 3D. I wasn't really expecting much from Bolt and I mainly went because I wanted to try out 3D. Many years ago I watched IMAX 3D at the Pacific Science Center in Seattle and I was quite impressed. It was exciting to see 3D technology available in ordinary cinemas. Bolt exceeded my expectations, and 3D failed to live up to them, but neither were a disappointment.

The trailers for Bolt made me imagine a movie that's amusing but shallow. I expected a storyline without much detail, and stereotypically cartoonish fun. I found a storyline with enough depth and detail so that it didn't seem at all hollow. There was certainly some stereotypically cartoonish fun, but there was far more to the movie, and it certainly seemed unique and creative.

The 3D effect was subtle but definite. With IMAX 3D, I remember things seeming to pop out far in front of the screen. With Bolt, I mostly just felt some subtle added depth information. It might have made the movie more engaging, and it might have even subconsciously made me feel better about it, but it generally wasn't amazing. On a few occasions when the 3D effect seemed underwhelming I removed the glasses to see distance between the two images, and it was surprisingly small. Some scenes were more impressive and a few felt intense. However, the intense feeling wasn't entirely pleasant, and on two such occasions I heard someone sitting nearby say it might make them sick. So, based on that, maybe high intensity needs to be avoided.

The glasses appeared new and they came sealed in their own plastic bag. I decided to keep them as a souvenir and for experimentation unless some notice told me I must return them. There was a message at the beginning to please return them for recycling, and there was a cardboard recycling bin for glasses at the exit, but nothing said that they were on loan and had to be returned. Therefore I decided to keep them.

(It's weird to say that's for recycling for environmental reasons. The environmentally sensible thing would probably be to reuse the glasses by inspecting, cleaning and disinfecting them. If they said they wanted the glasses back for reuse for environmental and/or cost-cutting reasons, I would have left my glasses behind. I wonder if they're using recycling and environmentalism as buzzwords that they expect people to be programmed to respond to.)

After coming home I already found one interesting thing about the glasses: they act differently based on the direction that light is coming from. If light comes from the front (as intended), rotating them changes most LCD screens from a blue tint to a yellow tint and back. If light comes from the back, the glasses behave more like polarized sunglasses, with the screen appearing normal when they are vertical and going almost totally black when they're horizontal, with only the dust on the screen glowing.

This led to me finally understanding circular polarizers. They consist of two components, a linear polarizer which selects for a particular linear polarization, and quarter wave plate which transforms light between linear and circular polarization. With the quarter wave plate before the polarizer, this combination selects for circularly polarized light by transforming it into linearly polarized light and then selecting for a particular linear polarization. This is what the RealD glasses do. The linear polarization of the output is irrelevant because human eyes don't see it any differently because of that. With the quarter wave plate after the polarizer, the combination selects for linearly polarized light and then circularly polarizes it. This is what camera circular polarizers do. To get the effect, one only needs to select for linearly polarized light. However, depending on orientation, linearly polarized output would reflect less from mirrors in the camera and cause problems, so the quarter-wave plate is used to transform it to circular polarization. The most serious problem would be through-the-lens (TTL) metering receiving less light, resulting in overexposed photos. Some cameras like typical non-SLR digital cameras do not have internal mirrors and they can work with linear polarizers (or even polarized sunglasses) without any problems.

The plastic pouch the glasses come in has multilingual and pictorial warnings not to use them as sunglasses. It is explained that they do not block UV light. Actually, wearing them outside would also be pointless because there is very little circular polarization in nature. For the familiar linear polarizing effect, the lenses are both backwards and sideways. So, for now I'm not sure what else I can do with these glasses, and they'll just be a souvenir. If I think of something interesting, I will probably post about it.

Finally, here's my favourite polarized photo, purely here as eye-candy: