This may be missing an optical element as the focal length appears to be negative. It may also need to be attached to whatever camera assembly it was intended for to achieve proper focal length. Multi element with fully coated optics. Rear clear lens diameter is 17.5mm, barrel is 23.5mm. Front clear lens diameter is 25mm, inside threaded barrel diameter is 33mm, outer barrel is 37.5mm. The entire lens assembly is 43mm long and the barrel is threaded halfway down with a diameter of 30mm. Unused in great original condition!