Special Summar lens (Leitz product number 42214) designed for tropical conditions. Almost unknown variant of the regular Summar (product number 42134) with an extra element at the front of the lens (optical formula B246a), which makes it a seven element lens. Leitz factory records indicate 'TROPEN' for these very few lenses, which are to be found among the late Summar lenses, shortly before the introduction of the Summitar. From outside visible difference is the ball and groove held collapsing barrel, as the Summitar lenses had. One of very few known to exist is illustrated in J.L. Lager's article in VIDOM. Included is a folder with the original Leitz blue-prints for this type of lens.
Photo credit: © WestLicht Photographica Auction