A portable overhead projector is a very reliable type of projector that can reflect images onto a wall or a projector screen. They are made up of a large box with a cooling fan and a very bright light. They have an extended arm above it and at the end of the arm there is a mirror that catches the light and reflects it onto the projector screen. The main use for the portable overhead projector is to enlarge an image and to display it onto a wall or a projector screen for an audience to view. A transparency is placed onto the overhead projector and it can be seen when projected onto the desired surface by the audience as well as the speaker. Although these kinds of projector were once were very popular in both business meetings and school classrooms, their use has been in decline recently as computer based projectors that are more sophisticated seem to be favoured. One of the first uses of the portable overhead projector dates back to World War II when it was seen as a great tool to aid the training of large groups of servicemen. During the 1950s and the 60s the overhead projector started to be used in the school classroom. Here it was used as a tool for educational purposes and then it crossed over and was used as a training tool in the business world. In the 1990s the overhead projector reached a peak in sales when nearly every business and classroom in America was using one. The best use of a portable overhead projector is when the screen or wall is around 2 to 4 metres (about 6 to 12 feet) away from the projector. There are some custom built overheads that allow the distance between the projector and projector screen to be increased but the cost of these may be a lot higher than the standard model. For ease of moving the projector around they can be placed into an overhead projector cart. The type of optics used can be seen as the biggest difference between different models of overhead projector and here are some of the main types that you can use: Folded Optics, also referred to as Chamber Optics. This type of optic has a mirror between the lamp and the lens. Some of the benefits of using a folded optic projector rather than using the more common direct optic projector are that the resolution is much higher and that there is a lot more light used to project the desired image. The light available with a folded optic projector is approximately 50% more than with a direct optic projector. The Reflected Light Optic. The lens of a reflected light optic is specially designed and it is backed by a mirror. The light source directs light to the lens and then the light gets reflected by the mirror. The reflected light gets directed back through the lens and then onto the main projective lens. Then the light is focused to a second mirror and finally onto the wall or projector screen. A portable overhead projector is most likely to have a reflected light optic, with the cooling system, the light source and the main projection optics being placed neatly into one unit. This way the complete unit can be folded down and placed into a case for ease of portability. In order to get the most out of your overhead projector when making any kind of presentation you ideally need a portable overhead projector, an overhead projector cart and a projector screen. The overhead projector is not as popular as it used to be when it was at its peak, but it is still in use in many business meetings and classrooms around the world. Although having said that, lots of users still prefer to use this type overhead projector in favour of the more sophisticated projectors because they are more reliable and a lot easier to use.
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