Overhead Projectors

Projecting transparencies, documents and 3D

An overhead projector was once an essential tool in any meeting place, and is still a common sight in classrooms. There are two main types of conventional overhead projectors - transmissive and reflective.

Transmissive overhead projectors are the ones with the lamp in their base. They tend to be bigger and heavier but are bright and produce sharp images. Reflective overhead projectors are more portable and have the light source in the head of the projector.

While traditional overhead projection is a proven system – effective and easy to use – standard overheads are being gradually replaced by digital machines as businesses and schools upgrade their technology.

Digital document cameras and visualizers

Digital overhead projection goes by many names. You may be familiar with them as video overheads, video presenters, visual presenters, visualizers, document imagers or document cameras. Using a small digital video camera, these overhead projectors take real-time video footage of a document or 3D object and project it onto a screen or interactive whiteboard. You can also connect a document camera to an external multimedia projector.

The main benefit of a digital overhead projector is that it allows you to project to a large number of people any number of detailed, full color images without having to scan them onto your computer first. That means you can project enlarged images of maps, photos and magazine pages, scientific experiments and a wide range of three dimensional objects. Of course, a digital visualizer also makes it easier to project basic text documents because you don’t have to run off the transparencies you would need for a conventional overhead.

The resolution of document cameras is generally quite good (XGA). Many models are compact and highly portable - great for taking on the road - and some have added features like focus, freeze (or image capture) and zoom. When you’re comparing document cameras you’ll want to look at image quality, color reproduction, zoom capability and, if you plan on projecting enlargements of 3D objects, depth of field.

Document cameras that allow adjustments to the lens head or light can help cut down on glare. The more advanced (and expensive) visualizers allow you to store frozen images, and some offer a split-screen feature so you can show that frozen image and a live image at the same time.

Modern opaque projectors perform similar tasks, allowing you to project non-transparent items like magazines, books and other documents or thin 3D objects. They tend to be heavier and larger, and generally don’t give you the digital video flexibility of a document camera.