The main purpose of an Elmo™ projector is to display documents and other objects that are not translucent -- in other words, documents that are not made with transparencies. These documents require a video camera and projection lens in order to work properly. The Elmo™ camera is usually digital. However, they are able to display more than just documents. In many cases, they can be used to display three-dimensional objects as well, though they will be rendered in two dimensions on the screen.
The thought behind the Elmo&trade projector is similar to that of the overhead projector, which came into widespread use during the late 1950s and continued through the 1990s. Such projectors were useful in making materials available to a wide audience in a classroom or group setting, but could only display documents put on transparent material. While duplication to transparencies is easily done, it required an additional step. Further, three-dimensional objects could not be displayed. They would instead be rendered as a black shadow in the area where they were blocking light from passing through.
The document projector changes all of those limitations. In fact, it is not only possible to display documents and objects on an Elmo™ projector, it is possible to even display moving pictures, such as movies. However, this is, by no means the most effective way of displaying such media. The camera used for a document projector does not operate with as many frames per second as standard video cameras. Thus, any movement would appear jumpy. That is one reason they are often called Elmo™ document cameras. It is understood that motion is not important in displaying documents.
Likewise, when looking at three-dimensional objects with Elmo™ document cameras, they should be kept still, or moved very slowly. Often, this is not a problem. If another side of the object needs displayed, it can simply be moved to face the camera. In such cases, the motion is not important and is only used to facilitate the change in the point of view.
