overheadkast

An overheadkast, also known as an overhead projector or overhead, is a device used to project images or text onto a screen from above. It consists of a light source, a lens system, and a translucent screen. The image is typically created on a transparency, which is a thin sheet of plastic or glass with the image or text printed on the reverse side. The transparency is placed on the stage of the overheadkast, and the light source illuminates it, projecting the image onto the screen below.

Overheadkasts were commonly used in educational settings, such as schools and universities, for presenting lectures and teaching materials. They were also used in business presentations and meetings. The device was popular in the mid-20th century but has since been largely replaced by digital projectors and other presentation technologies.

The overheadkast was invented in the early 20th century and has undergone several iterations and improvements over the years. Early models were manual, requiring the user to adjust the focus and brightness settings. Later models introduced automatic focusing and brightness control, making them easier to use. Some overheadkasts also featured built-in lamps and screens, eliminating the need for external equipment.

Despite their decline in popularity, overheadkasts are still used in some educational and professional settings. They are also collected by enthusiasts and used in retro-themed presentations and events. The overheadkast is a significant piece of educational and technological history, representing a key stage in the evolution of presentation technologies.