Why do you need special glasses for 3-D movies?

Dear Cecil: I’m sitting here placing cold compresses on my eyes after being suckered into another 3-D movie. After being tortured as a child with those ridiculous candy-wrapper glasses, you’d think I’d learn, but nooooo. Though the movie, Space Hunter, was the most natural, i.e., it wasn’t hitting you in the face at every turn with special effects, it still fell victim to the low state of 3-D technology. Is there a reason, save Foster Grant’s special interest, that we must suffer through the present form of projection? Why can’t a coherent 3-D image just appear on the screen? John F., Evanston, Illinois

Cecil replies:

John, you knucklehead, think about it. The movie screen is flat! Reality is 3-D! There is a basic problem trying to get a 3-D image to “just appear” on a 2-D surface. What you have to do is fool the eye by presenting each eyeball with a slightly different image, which the brain then fuses into the illusion of 3-D. (Remember those old Viewmaster 3-D image viewers? They worked the same way.)

To create a 3-D movie, two images are projected simultaneously, one for each eye. You wear special glasses with different-colored lenses so that one eye sees one image, the other eye sees the other. Voila, 3-D action–plus untold misery as the glasses dig into your nose. But hey, what’s your complaint? Haven’t you heard of suffering for your art?

For years one heard rumors of an experimental 3-D screen that made glasses unnecessary. (Supposedly it worked along the lines of those novelty photos where the image changed as you looked at the thing from different angles.) However, as far as I can tell, this process is never became commercially practical.

The main problem with Space Hunter, in any event, was not the glasses but the print. Years ago 3-D required two separate projectors, which were hard to keep properly aligned and in sync. To eliminate such problems, Space Hunter used a new process in which both images were printed on the same piece of film. Unfortunately, since you were still using the same old 35mm stock, each image got to be only half as big as before, and consequently was a lot fuzzier when it got enlarged to big-screen size. In addition, since you only had one light source (as opposed to two with the old 3-D system), the screen image was a lot dimmer. The result was eyestrain and migraine headaches for viewing audiences around the country.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.