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Ghost image debugging on a 240-degree fisheye lens

For cartography applications Frank Data R&D developed a new concept for taking measurements which consists in obtaining panoramic photographs, which are later scanned into a computer. The computer then processes consequent pictures from different locations and creates 3D images of the landscape. An extremely wide angle Fisheye Lens is part of this concept. Delft Instruments has designed and manufactured this lens. The specifications and design drivers are discussed. Under extreme sun illumination conditions ghost images may occur, which will be presented with photographs. Not all of these effects could be traced by experiments. The trace was then continued by computer simulation based on the ASAP software. A method of debugging such a lens is presented. A Fisheye Lens is characterized by a small entrance pupil, compared with the size of the first lens, at a field-depending position. Together with the number of 18 optical surfaces in this case and the large field of view, a tremendous amount of ray tracing was necessary to find out the surfaces and the conditions that lead to the ghost images. Although a powerful workstation was used, an efficient strategy was necessary to isolate the main contributing paths and to visualize them.