Summitar * 2/5cm Summicron prototype 'Kruckenhauser'

Beautiful very rare prototype of the later Summicron lens with Thorium-oxide element, note the diaphragm with apertures to f:22, a small series of these lenses was produced for testing purposes in 1950, three years before the Summicron came on to the market, the lens here is in absolute mint, original condition, optics showing some haze and focusing not 100% correct, with both caps, Leica records show that this lens was delivered to the Austrian photographer and 'ski Pope' Stefan Kruckenhauser, famous for his innovative winter pictures with 35mm cameras and skiing techniques, he also received the pre-series Leica M3 no.700000!