Lens unit with self-cleaning characteristics

摘要

Several lenses (L1,L2) are contained in a cylindrical housing (11), the second one being behind and clear of the first, which is closest to the target. The distance ring (11) holding the lenses apart is of material with higher heat-conductivity than the lenses. At its inner edge it has a non-flat moisture-separation surface (17a), which increases the surface area at this edge. The housing material can be of high heat-conductivity, being mounted on an optical display system. The front part (1a) of the housing is exposed. The separating surface can be of concave-curved cross-section in the axial direction.