# A 3-D Primer

## Article excerpt

For those who know nothing about 3-D, a basic course-For those who know everything about 3-D, a refresher

Every book written on stereo photography has the first chapter devoted to explaining what 3-D is and how we see it. Every magazine article and monograph on the subject (with the exception of some technical articles) has the first paragraph assigned to basics. So why am I writing this? With all this deluge of information (for those who are interested), coupled with the fact that some of the people who will read this article may know more about the practical ends of stereoscopic motion picture production than I do, why another 3-D primer? The reason is twofold: (A) to explain 3-D to those who have only a sketchy idea of what it is, in order that they may gain a clearer understanding of the other articles in this issue of American Cinematographer, and for their own enlightenment should they encounter it in theory or practice in the future, and (B) to present some ideas or angles that perhaps may be new to the dyed-in-the-wool 3-D veteran.

What is 3-D and how do we see it?

The classical definition of what 3-D is goes something like this: "When we look at the world around us, we see it with two viewpoints at the same time, our two eyes. Because of this, we are able to see not only the height and width of things around us, but also their depth and distances from us and each other. We are able to see all three dimensions; hence the term '3-D/ Try this simple experiment: cover one eye with your hand and look around you. Notice how flat everything looks? Now uncover your eye. Notice how everything jumps back into proper perspective? Each of our two eyes picks up a slightly different view of the world. To prove it, close one eye and hold a finger up about a foot and a half from you. Look at some distant object and place your finger in the way. Keep looking at the far object and open the other eye as you close the first one. see how your finger apparently jumps aside? This apparent displacement is called parallax, and it is the proof that we receive two discrete views of whatever we look at. The brain combines these two, essentially flat, views into one stereoscopic view."

For professional consideration, the classical definition falls down in these areas:

1. The results of the experiments we are asked to perform beg that we infer that all that is needed for lifelike 3-D perception is two views of the subject. This can easily be seen to be false by anyone who has seen a narrow-screen 3-D film. There is stereo relief, but without the peripheral experience widescreen systems give, realism is found to be lacking. This peripheral image is so important that in the early fifties, 20th Century Fox was advertising Cinemascope as being 3-D (or very close to it).

2. The results of the experiments beg that we infer that one-eyed people cannot judge depth and distance. In actuality this is not the case at all, and here is an "anti-experiment" experiment to prove it: cover one eye and get up and walk around the room. Walk into another room. Do you have any trouble judging distances? Sit down. Did you miss the chair because you were unable to judge its distance or position? No, of course not. Much depth judging is done by shading, relative size, and other non-stereo visual cues. And if you normally use two eyes, you have had considerably less experience in getting along with only one than one-eyed people have. And not incidentally. Andre de Toth, director of "HOUSE OF WAX", one of the finest 3-D motion pictures ever made, both technically and artistically, has only one eye.

3. The definition begs us to infer that one cannot judge relative depth and distance in a flat-screen motion picture -a particularly unfriendly inference for cameramen, since the cinematographer on a flat picture strives to put depth into it by lighting, selective focus, composition, etc. The audience can tell who's standing in front of whom and how far away from the train the Indians are; if they couldn't, the Director of Photography would have fallen down on his job. …