The Flannan Isles optic was a hyper-radial - that being the largest size of lens to be found in a lighthouse. Sadly with automation in 1971 the magnificent lens was purposely destroyed by the keepers as ordered by HQ. The lens was perhaps too big to be taken off the rock, so the glass was smashed out of the weighty brass panels. The brass was taken ashore and allegedly sold for scrap. This prism was salvaged by a keeper and made into a gift for one of his colleagues.