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Right between the eyes II
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Published Wednesday, December 29, 2010 @ 7:51 PM EST
Dec 29 2010

It turns out my decrepit ocular system and aging brain can, in fact, process two polarized images and generate a stereoscopic one.

The problem is I'm extremely myopic, or nearsighted. Myopia happens when the eye focuses incoming light not on the retina, but at a point in front of it. In short, my eyballs are too long. The corrective lenses I've worn since fourth grade shift the focus back to my retinas' surfaces and make it possible for me not to have to live like a human mole.

Most people with myopia require a -1 to -3 diopter correction to achieve normal vision. I need -9.25 diopter for my right eye and -8.25 for my left.

The minus sign in front of the diopter value indicates that in shifting the focal point backward, the image will be reduced in size, rather than magnified. A +10 diopter lens makes a decent magnifying glass. The -9.25 diopter lens needed to correct the vision in my right eye significantly reduces the size of the image passing through it:

What this means is that the objects I see, while in sharp focus, appear significantly smaller to me than they would to someone who doesn't wear glasses. It also means I have a broader field of view. I like to think of it as having CinemaScope vision, but having to sit in the last row of the theater.

It gets better. Like most people over the age of 40, I have presbyopia, which means my eyes have lost their elasticity and have difficulty focusing close-up. To compensate for this, I wear progressive lenses- "lineless" bifocals.

The corrective value varies gradually moving down from the center of the lens, until an additional +2.50 is reached at the bottom. The top provides my distance vision; the bottom my near vision correction.

With all these optical gymnastics, it's no surprise the performance of the lenses aren't linear. As you move away from the strip down the center of the lens, various aberrations and distortions occur. Watch progressive lens wearers, and you'll notice that if they're doing something that requires high visual acuity, they'll move their heads instead of their eyes in order to maintain the optical "sweet spot" in the center of the lens that provides the clearest vision.

So what does this have to do with watching 3D movies?

I think the problem is optical overload. The projected image requires polarized lenses to isolate what each eye should see. I have to place the 3D glasses over my prescription lenses, which undoubtedly causes shifts in the correction.

Then there's the progressive lens problem. I have to look through the very top of the lens to get undistorted distance vision, but even the top of the lens has variations that caused the 3D image to distort or drop out in some places.

It would be nice if the industry would standardize on a single 3D process, and perhaps sell polarized corrective lenses to movie fans at cost. If the 3D fad continues, I may consider buying a pair of fixed focal length lenses strictly for distance (and movie theater) viewing.

That said, the 3D effects in Tron: Legacy were superb. While the IMAX theaters popping up in multiplexes aren't "real" IMAX (huge screens and 70mm film projection), they represent the best presentation of a movie you're likely to see. The screen is a bit bigger than the normal multiplex, and is located closer to the audience to provide a more immersive effect. IMAX digital projectors generate about a third more light output than standard units, and for 3D, two projectors are used. People often complain about the dimness of 3D films. The picture looked sharp and vibrant to me. And if the pretty pictures don't get your attention, the 14,000 watt sound system certainly will.

As for the movie itself- well, you'll either get it, or you won't. If you do, you'll want to see it multiple times. Forget the complaints about plot and characters. The Thunderbolt has neither, yet it's still a kick-ass experience.

Ditto for Tron.


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