a multi - lens system provides a plurality of sensitive areas of even size over a wide panoramic field of view and reduces an exposure height of the system above an installation plane , yet assuring successful motion detection . the system has a dome - shaped shell with a plurality of convex lenses for collecting infrared radiation from the panoramic field of view to an optical detector positioned in a focal region . the lenses are distributed over a wide solid angular range to give the discrete sensitive areas . the focal region is offset towards a vertex of the shell from a point where optical axes of the outermost lenses at a maximum solid angle about the center axis intersect with each other . thus , the outer lens at a greater angular disposition has a greater distance to the detector so that it could define its own sensitive area closer in size to the adjacent sensitive area defined by the adjacent lens at a less angular disposition , enabling to equalizing the discrete sensitive areas . further , the exposure height of the system i . e ., a vertical distance between the vertex of the shell and the outermost lens is reduced to achieve a low - profile installation design . the lens at a greater angular disposition about the center axis is set to have a greater focal length so as to provide an effective image spot in the focal region for detection of infrared radiation through each lens by the detector , thereby assuring a consistent motion detection over a widely distributed sensitive areas .