Fisheye supplementary lens for liquid crystal projector

In some applications the large field-of-view projector is demanded for special purpose. However, currently available liquid-crystal-projectors generally have a field-of-view of 40 degree. These ordinary projectors can't meet the special requirements. The ordinary method for solving the problem is to remove the original projection lens and design a new fisheye lens whose field-of-view is large enough to meet the requirement. However, most current advanced projector's lenses are integrated with the circuit controllers or circuit boards. In many situations it is impossible to replace the lenses. In this paper, a new method, designing a new supplementary lens for the original projector without destroying its structure, is presented. The field-of-view of the new system can be expanded to 180 degree. Since the exit beam of the original projector lens is similar to parallel beam, the entrance beam of the supplementary lens is also parallel beam. That means, both the entrance and the exit beams of the supplementary lens are parallel beams. So the supplementary lens can be treated as a telephoto system. In this paper, the focal length of the original projector lens is 16.4 millimeter, the field-of-view is 42 degree, and the required field of view is 180 degree. The new designed supplementary lens is a reverse Galilean telephoto system. The software Zemax is used to design the system. Results show that the system is well designed and it can meet the actual requirements.