The f/3.5 50mm is a reversed Tessar type with four elements in three groups, with the last elements reversed in power from the original Tessar design. The f/3.5 90mm is a triplet and the f/3.8 135mm is a straightforward Tele-Tessar design. The longest manufacturered lens in the series, the f/4.5 153mm, has a double negative cemented pair behind the stop. The f/3.5 35mm is a Heliar design of five elements in three groups, very similar to the f/3.5 100mm Ektar used on the Medalist, both designed by Fred Altman. Apparently Kodak had planned a super tele of about 250mm, since the variable viewfinder has a setting for 254mm. Neither the glossy Ektra prospectus, published on the camera's release in 1941, nor the "Kodak Lenses" section of the Kodak Reference Manual, published originally in 1942, have any mention of this long lens, though I have heard unsubstantiated claims that there was at least one prototype. The f/1.9 50mm is a variation of the Biotar design, originally used in the f/2.0 45mm Ektar mounted on the Bantam Special. Of these lenses, the f/3.5 50mm andf/3.5 35mm are reputed to be the sharpest, with the f/1.9 50mm said to have the poorest performance. All Ektra lenses attach to the body with a screw mount that locks when snug. Two key ways on the mount make lens orientation a no-brainer with the body in any position.

While Kodak had begun treating air-glass surfaces in the late 30s, I can only find documented evidence of their Lumenized coating of magnesium floride in lens manufacturer of the late 40s. The lens section of the Kodak reference manual, printed in 1945 (second edition?) does not include Lumenized lenses, while the separate Kodak Data Book, Kodak Lenses, Shutters and Portra Lenses, 3rd Edition (1948) describes the process, but no longer includes the Ektra lenses. In his 1951 book, Lenses in Photography, Rudolf Kingslake, Director of Optical Design for Kodak, reports that calcium flouride, as an optical coating, was first offered for commercial use in 1938, but its softness relegated it to inner surfaces. The magnesium flouride that could be deposited on glass and which was as hard as the glass itself, was adopted in the 40s. Whether later Ektra Ektars ever had this coating is for me an open question. More general information on Ektar lenses.