Zoom projection lens

Zoom projection lenses have been designed that have an entrance pupil that remains stationary during zooming and an operative aperture stop distinct from the system's physical stop that moves through the lens surfaces as zooming takes place. The fixed entrance pupil allows for efficient coupling to the light source throughout the magnification change. By allowing the stop to move through the lens, the lens element sizes and aberration contributions can be minimized. The concept of the operative stop can be employed for both positive and negative first-group configurations. For wide angle projection of 64 degrees total angle, a lens system with a negative front group followed by a positive zooming group has been designed with a relative aperture of f/4.5. Applications involving large LCD panels as light valves require the use of plastic optical materials with aspherical surfaces to minimize manufacturing costs. Concentrated high wattage light sources introduce temperature variations that impose additional constraints on the optical design. By combining plastic and glass elements the image position and aberration correction are stabilized throughout a plus or minus 25 degree Celsius temperature change.