lenses of the same general construction are often given a name implying this design. for example, a tessar always has four elements in three groups as described below, although tessars have been produced with different focal lengths and maximum apertures for many decades. sometimes a name does not identify a specific design; kodak's ektar lens brand name encompasses many different types. sometimes different manufacturers use different names for lenses of the same type; for example the voigtländer skopar is of tessar design. and sometimes identical lenses are sold under different names and at different prices; for example, lenses branded as rodenstock and caltar.