The Caltar IIN series are the very same lenses as the Rodenstock APO Sironar N and Grandagon N, just engraved differently and sold by Calumet. Calumet is a large educational supplier and a large fraction of Caltar IINs that come up on the used market have seen minimal use. Brand name recognition being what it is the Caltars are real bargains in the used marketplace. The 210mm f/5.6 ones (301mm IC) routinely sell for less than $200 in pristine condition on eBay. Mine is exquisite--as is my 135mm Caltar IIN.
Yes, I noticed very attractive prices and also was wondering who made them. Good to know.