![]() ![]() If you're not planning on mounting your projector to the ceiling then a short throw lens would allow you to remove the projector from the seating area of your students. If your projector has a large throw ratio then that means you have a more tightly focused optical system. This can be an ideal setup in a classroom as it allows a teacher more mobility. Projectors with short throw or super short throw lenses are able to create larger images at a shorter throw distance. Much like a professional camera, projectors with optional lenses can generally provide solutions for any special need albeit at a higher cost. The range of projector zoom ratios are as low as 0.4 and as high as 2.1 however, you can go lower and considerably higher by purchasing a projector that supports optional lenses. With a 1.2 zoom ratio you can vary the image size by 20% by simply adjusting the zoom lens as illustrated in the graphic to this graphic. The most common zoom ratio among today's projectors is 1.2. And finally, if you should decide to switch to a smaller or larger screen in a fixed installation, you have a reasonable chance of making this change without having to move the projector. ![]() Second, if you are using it in a fixed installation, a zoom lens gives you greater flexibility on where you can install the projector. First, if this is a mobile projector, a zoom lens is extremely handy for setting up in rooms where you have little control over the size of the screen or where you must place the projector. So why would you want to do that? There are a several reasons. It allows you to increase or decrease the size of the projected image without moving the projector. It essentially let's you make the object bigger or smaller without you moving. ![]() If you've ever owned a camera or camcorder, you have no doubt had the ability to zoom in or out on the object you're trying to photograph. So what about zoom ratio? What is it and how does it affect the throw distance and image width? If the projector you choose has a different throw ratio, use this formula to compute throw distance or image width. So the throw ratio is a simple formula that let's you easily compute throw distance or image width given that you know one of these measurements. Conversely if my distance from the screen is 20 feet then my image must be 10 feet wide. So if I'm using a projector with a throw ratio of 2.0 and I have an image width of 5 feet, then my throw distance must be 10 feet. This means that for each foot of image width, the projector needs to be 2 feet away or D/W = 2/1 = 2.0. So for example, the most common projector throw ratio is 2.0. For any given projector, the width of the image (W) relative to the throw distance (D) is know as the throw ratio D/W. This distance determines where the projector will sit in your classroom relative to the projection screen. Throw distance is the distance from the tip of the projector's lens to the screen. ![]()
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