As others mentioned, the Xenars were Schneider's version of the famous Zeiss Tessar. They went into production in the early 1920s (basically, as soon as the patent expired on the genuine Tessar) and remained in production until the late 1990s. I think production officially ended in 1998, but I still occasionally see a new one listed for sale. So, some may still be "in the channel".
The last two focal lengths offered were the 150mm f5.6 and 210mm f6.1 Xenars. These late Xenars are great little lenses - smaller and more compact than the older f4.5 versions. The 150mm is a bit tight on 4x5, but it does cover with a bit left for movements (173mm IC). The 210mm makes a great compact lens (46mm filters, Copal No. 1 shutter) for use with a 4x5 field camera and will even cover 5x7 with room for modest movements (249mm IC). There was also a later model 300mm f5.6 Xenar that was made throughout the 1980s and possibly into the early 1990s. It came in a Copal No. 3 shutter, but was still a lot smaller and more compact (67mm filters) than the standard f5.6 plasmat. Coverage was sufficient for 8x10 with modest movements (347mm IC).
As Jim mentioned, for a brief period during the mid-1980s, re-badged Xenars were sold by Calumet under the Caltar Pro name. However, not all Caltar Pro lenses are Xenars. Some of the Caltar Pro series were made by Komura in Japan. The easiest way to identify the Schneider-made members of the Caltar Pro line is that they are engraved "Made in Germany" around the lens barrel.
Other fairly recent Tessar-types include the Fujinon L series (210mm f5.6, 300mm f5.6 and 420mm f8) the 150mm f6.3 Fujinon W and the superb Nikkor M series (multicoated and available in 105mm f3.5, 200m f8, 300mm f9 and 450mm f9 focal lengths). The East German state owned VEB Carl Zeiss Jena continued to make Tessars up until the reunification of Germany in the early 1990s. These lenses, in barrel mount, regulary show uop on eBay at affordable prices. After the reunification, Docter Optics continued to make Tessars, but offered them in modern Copal shutters, until the death of Bernhard Docter and subsequent bankruptcy of his company in the mid-1990s.
The Tessar is the most copied lens design in the history of photography. Tessar-type lenses have been made by just about every manufacturer to ever make camera lenses - for all formats from sub-miniature up to ulatra large format. While the coverage is less than the modern plasmat types, the perfomance is generally excellent out to about 60 degrees (a bit more or a bit less depending on the implementation), and the simple design is relatively inexpensive to produce. With only 4 elements in 3 groups, it is also possible to make Tessar types that are very small and compact for their focal lengths (lenses like the 150mm f5.6 Xenar, 150mm f6.3 Fujinon W, 200mm Nikkor M, and 300mm Nikkor M are some of the lightest, most compact LF lenses ever made in their respective focal lengths). The Tessar design is over 100 years old, but still going strong.
Kerry
