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Overhead projectors (OHPs) and accessories
An overhead projector is a device for displaying transparencies, transparent sheets onto which text and images is printed or hand-written/drawn. An overhead projector consists of a box containing one or more very bright lamps covered with a collimating lens – i.e. a lens which renders light rays nearly parallel – and an arm on which there is a mirror and lens. A transparency is placed on the box and through it light travels, reflecting off the mirror onto a screen. The image is thus projected.
Overhead projectors were first used by the US army in 1945 to train recruits. Usage of OHPs became widespread in schools and businesses in the late 1950s and 1960s. Despite the inexorable march of computing technology, in particular of presentation software, overhead projectors continue to be used for education, training and presentation purposes. Of course technological developments have entailed great improvements in presentation techniques. However, OHPs remain a good stand-in in the event of computer failure and in fact many presenters prepare both Powerpoint and transparency presentations for their lectures. Further, with an overhead projector there is the added facility for live writing – presenters can write on the transparency as they speak and, using a non-permanent marker, the transparency can be washed afterwards and reused.
We sell budget, standard and portable projectors from 3M. All OHPs have two bulbs in case one fails. Our portable overhead projector only weighs 5.4kg!
In addition to overhead projectors themselves we supply a full complement of OHP film so that you can print your transparencies in ink jet and laser printers and photocopiers. Or we have write-on film. We also supply transparency protectors (frames) to protect your transparencies from fingermarks and scratches.