The clockwork operated revolving dioptric light was constructed by Chance Brothers. On 3 September 1985 at 00&colon;00 hours the "Dioptric Surveyor" departed in a storm. Concave lenses have negative dioptric value and generally correct myopia (nearsightedness). The original lens, still present, is a first order Chance Bros. sixteen-panel Fresnel lens dioptric. The dioptric lens was of the 6th order and the range was 8 nautical miles. Chance Bros dioptric lens or a four panel AGA catadioptric lens on an AGA pedestal. The original dioptric lens, which was subsequently replaced, is now on display inside the castle. In 1851 Robert's son, Alan Stevenson, installed a first order dioptric lens at Kinnaird Head. In 1865, the light source was improved from catoptric to first order dioptric.