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Tech Tip

Understanding f value in projector lenses

The f value of a projection lens is a ratio of the focal length to diameter. Knowing only the area of the aperture requires also knowing the length of the lens also to be informative as to the amount of light coming through the lens. Lenses are referred to by their maximum aperture. Lenses which have wide apertures and can throughput the maximum projection light are called fast lenses. Lenses which throughput less light at their maximum apertures are called slow lenses. As you increase the SWR throw distance of the lens , the size of the lens will increase in order to maintain a low (fast) f value.